c-attack

It should be swappable.  The cap is a thin plate bolted to the outside like a lens.  The original Elite Capellix models came with two interchangeable versions.  If you don't like that silk screen decoration, it should be a 2 min change.  

Yes. All the Corsair Vengeance/Dominator series have a readable sensor on the module. It can be read by CUE or any of the common monitoring programs. 

You won’t be able to notice a performance difference between the two fans. You can choose based on appearance. The A12 is going to be slightly quieter between 1000-1500 rpm because of the difference in blade design. Above 1500 everything is somewhat loud. 
 
Remember the pump speed you are shown is a running prediction based on the revolutions recorded in a 2 second interval. So if it records 73 revolutions in 2 sec, that’s 2190 rpm and 74 in 2 sec is 2220 rpm. These are small fractions of a very high speed device. No pump reads 2200-2200-2200-2200 every 2 seconds. That level of precision is not needed in a product like this nor does change the actual flow rate which is really what matters. A significant pump drop is several hundred rpm indicating the pump clearly slowed down, lost power, or is fighting against noticeable pressure (continued operation under expected speed). 

SP-Elite - Yes. PWM fan and 8 led fan series for RGB. 
 
SP-Pro - Yes, for RGB (8 led fan series). No for speed control. DC motor. Will be stuck at maximum. 
 
SP-RGB - No and no. Wrong motor. Wrong led type. These don’t work with any of the new controllers and are discontinued. Still some out there is the wild on shelves. 

The SP-Elite is lighting compatible.  It has 8 center hub LEDs like the SP-Pro and will look nearly identical. CUE does not distinguish the Sp-Pro, SP-Elite, ML-Elite, or AF-Elite. They are all “8 led fan series” and can be mixed freely. 
 
The only notable difference is the new SP-Elite will be a PWM motor. Your motherboard should have no issue with that, but you can’t use it it on a splitter with the other two SP-Pro for speed control. 

I see a couple of cosmetic differences on the underlying PCB, but that isn't too surprising if these were manufactured months/years apart.  While slightly less prevalent on DDR4 compared to DDR5, the underlying IC and materials can change from manufacturing run to manufacturing run.  So 18 months apart maybe the PCB supplier is different or they changed the PCB manufacturing process.  What is more amazing and important is the version is the same across the time gap, so it should be the IC for both sets.  The new RAM should behave very much like the old RAM for settings and voltage.  

7 fans?  Or 7 devices?  
 
All Corsair controllers have a maximum of 6 fan control. In order to use a 7th fan, you’ll need a second controller and you’ll need to break the 7 up into logical groups (6+1, 4+3, etc) for your case. Each group will be a separate working lighting unit, so if you prefer moving patterns it may better to do a 3+4 split rather than have the rear exhaust be all on its own. 
 
There are RGB fan splitters out there and you should be able to use one to incorporate the 7th fan. However, be aware this will twin two of your fans so it’s not a great setup if you like the moving patterns. 

There are not too many legacy devices left, except a couple of 8 year old mice or headsets. The H100i v2 is supported in CUE 4. 
 
On the other hand, if the H100i v2 is the only CUE device, there isn’t going to be much gain moving to CUE 4. It will be a new interface to learn, but he won’t gain any extra functionality or options for the H100i v2 that was originally a legacy device. CUE 3 ended development about 3 years ago and the only kind of updates you’ll see is if Microsoft pulls one their pranks and everyone has to do security updates. There isn’t any need to check for updates through the app. 
 
The counter-argument is if he picks up any new gear it will need CUE 4 to work for anything released in the last three years. Maybe he will like the new interface better?  It is a bit lighter on resources. The final option is if the H100i v2 is the only device, he doesn’t need CUE at all for day to day running. It automatically saves the fan curve choice and pump speed. All he can really do in CUE is change the pump lighting. So if the program mostly sits in the background, he can set the app not to run on start up, then only launch when he wants to change color, then quit the app again. Cooling performance is unchanged. 
 
If you do go forward, download the 4.33 file through the website and install manually. 

Why should the fan be changing speed at that moment?  Your 3 pin fans are not controllable.  They are missing the 4th control wire/pin and will be stuck at maximum any time they have power on that controller.  The Commander XT is a PWM only controller.  The Commander Pro is DC and PWM capable.
 
In the second screenshot, you are showing us a single fan of unknown make or model and attempting to run it in zero RPM mode.  Not all fans are capable of running at 0 rpm without a voltage turn off.  Regardless of whether it is capable of zero RPM, the end result will be either a flatline 0 or the minimum possible speed of the fan at it's lowest PWM level.  
 
If you want to demonstrate control or lack thereof, click the yellow + and create a custom fan curve.  That will open the settings for fixed RPM and fixed PWM %.  Then you can enter various percentages or speeds to see if the fans respond to command.  

The setting just below that one....  5600 G2 (5600 x 1.00).  The one you're on is using a 1.33 strap which affects all clocks, including CPU frequency.  Most users want to avoid that and it can create some unexpected limitations.  You want the normal 1.00 modifier.  The "G" is for gear and anyone on DDR5 is and above 4000 is going to be on Gear 2.  You do not want Gear 4 for normal frequencies and it will reduce performance.  I don't use MSI boards, but that is a lot to take in for the normal menu.  If you F7 back to the "E-Z BIOS", it likely will take away a lot of those fringe choices that most users do not need.  

The fans are interchangeable. The Elite Capellix AIO models come with a Commander Core controller that provides PWM speed control and RGB control for 6 Corsair fans of any type, including mixed sets. The Commander Core also powers and controls the pump. 
 
QL to replace the AF Elite RGB is a straight swap. True plug and play and controller will auto-detect type. Does a QL move as much air though a radiator as an AF?  No, but not to the point where you should care. The larger your radiator surface area, the less important fan choice becomes.  With a 360mm radiator fan choice and coolant temp changes are to be a tiny part of the CPU temp. You will be voltage limited on how hard you can push the 13900KS. A 1-1.5C difference on fan choice will not matter and QL fans have a lot of extra presets that use the rings and are otherwise not possible on center hub LED fans. The only exception I might concede here is if you do folding or long CPU renders where the CPU is going run max power for hours at a time. In those setups you probably should take all possible advantages. 

This is an indicator the pump is not moving water through the CPU block.  Physical contact errors create instantons temperature change that rises and falls with voltage.  If you get to the BIOS and see it skipping upwards like this, that's the water trapped in the CPU block heating up in rapid fashion.
 
The CPU Fan Boot error is doing its job.  It's telling you the H100i v2 pump is not talking back to the BIOS and it's throwing the error at you as a warning.  This is most likely going to be an electrical failure of some type in the unit (no user fix), but if you accidentally set the voltage for CPU fan to "auto" or one of the typical CPU air cooler fan profiles, it's possible that won't create enough voltage to star the pump.  Since you've already checked on this, it's seems highly likely this unit just reached end of life.  Check your purchase date.  A 5 year warranty is a long time and while there won't be any more H100i v2 around, they will send you a more current replacement.  Corsair Support link is as the bottom of the page.

It's showing you a preview of what it will look like on boot and shutdown.  When you leave one channel it stops previewing and shows the other.  Remember Hardware Lighting is for when CUE is not running.  It has more basic choices and those effects must be saved and run from the controller.  You need to be working in "Lighting Effects" to get the full range of options for when CUE is running.
 
 
That will be on the Commander Pro.  Unlike the Commander Core, it doesn't have a built in temp sensor for sensible fan control.  It will default to CPU temp (something available on any PC) but use a liquid temperature control range for AIO or custom cooling.  That keeps the fans running around 1500 all the time. 
 
1) Go to the Commander Pro and the "Cooling" tab.  Click on the yellow + to create a new custom cooling mode.
2) A graph will appear below.  Go under it and select one of the three 'shape tools'.  Those correspond to the Quiet/Balanced/Extreme presets on the Commander Core.  
3) The Quiet one is fine to start.  Immediately change the sensor choice to "H150i Elite Capellix Temp" or however it lists the AIO.  This will make them do the same thing as the fans on the Commander Core and liquid temp is a good general control variable for all case fans.
4) Be aware when you quit CUE, you will break the connection between the two Commanders and the C-Pro fans will ramp back up again.  There is a more elaborate solution for that involving the temperature probes from the Commander Pro box, but not all users need that.  If you spend a lot of time outside the OS or have a light sleeper nearby, then it is probably worthwhile.  
5) You can fine tune the curve by clicking on any dot and then entering a new RPM value in the box.  Don't be afraid to push the baseline lower or limit the top end.  Water cooled systems do not overheat because you cap the fans at 1200 rpm vs 1400 or 600 vs 800.  Always choose based on noise.  This applied to both controllers.  Fans affect the liquid temperature.  +-1 to H150i elite temp is only +-1 to CPU temp.  Nobody really cares if the CPU is -2C cooler when playing a game unless you are maxed out.  +200 rpm is a bad trade for -2C if it seems noisy.  

CUE seems to think you may have this cooler, the H100i Elite.  It has AF-Elite fans do have a ~1850 rpm max.
https://www.corsair.com/us/en/Categories/Products/Liquid-Cooling/iCUE-RGB-ELITE-Liquid-CPU-Cooler/p/CW-9060058-WW#tab-tech-specs
 
Possible you have the wrong model number?  The AF fans on the Elite will be easy to identify.  The pump ring on the Elite is going to be a lot more vibrant compared to the older XT models.  The pump lighting should also give it away.  The new Elite has a much more complex pattern as seen on the product page.  
 

For your motherboard USB definitions, you'll need to look that up in the manual or hope someone else here has Dark Hero X??? series.
 
Connectivity - It seems like you will have 8 x 8 LED fans.  This will require two controllers.  The Commander Core in the AIO kit is mandatory and provides power for the pump.  There is PWM and RGB control for 6 fans.  You will only need one RGB controller more.  You can use the Lighting Node Core from the triple pack or the 'bare bones' stripped down one in the case.  Each controller will act like it's own lighting group.  You will split the fans they way you want them to be grouped among the two controllers.  For the PWM side, you should also have a 6 fan PWM 'repeater'.  This is effectively a powered 6 way splitter for speed control.  You will connect 3 of the AF fans to this (any three on a panel is fine), then it connects back to the Commander Core PWM side.  All three will run the same speed, but not an issue for any bank of three on the front or top.
 
Commander Core = 1 USB 2
Lighting Node Core= 1 USB 2
LCD top will share with Commander Core
PSU = 1 USB 2
 
The Corsair 4 port internal USB hub is designed to help with this.  There are also other brands and this is a not a brand specific device.  

If swap it over to fan 2 or 3 and it still doesn't spin, it's going to be the fan.  Could be a break or defect in the wire, connector, or rarely the motor.  Usually with those you hear it coming before it stops.  You can contact Corsair Support and see about a replacement under the warranty terms.  I don't think they do a different warranty on the fans vs the pump/radiator, etc.  The other option and likely the speedier one is to pick up any PWM radiator appropriate fan.  The tricky bit is getting something to match.  The XT stock fans are black frame, gray ML blades and the same as this "twin pack" below, but of course you don't need two.  The individual retail models tend to be black but any ML-Pro 120mm black or AF120mm black will be fine too.  And I suppose if you were interested in RGB fans, this would be the moment to change over.  
 
https://www.amazon.com/Corsair-Premium-Magnetic-Levitation-2-Pack/dp/B01G5I6MRK/ref=sr_1_2?crid=11RYSUXZX02BT

Assuming all 10 fans are RGB models, you will need two RGB controllers. While I prefer to use a Commander Pro for its 4 sensor inputs, not everyone needs that many and the real decider here is what you have for fans. The Commander Pro and Lighting Node Pro use a 5v booster called a RGB lighting hub to deliver extra power and thus you can run 12 RGB fans (2x6) from a Commander Pro. However, most newer fan models don’t come with RGB hubs anymore and the current system is the direct connect Commander Core and XT controllers. So if you are buying SP-Elite, ML-Elite, AF RGB, or QL fans, you likely want 2 Commander XT controllers for 12 PWM and 12 direct RGB connections. Those fans do not have RGB lighting hubs in the box. 
 
However, that is not the only way to do it. You can cut out a Commander XT and use a Lighting Node Core from a fan multipack as the RGB controller and then the case included (or any other) pwm hub as a powered splitter. The potential advantage here is the LNCore is smaller than a Com XT for squeezing it in back. Additionally, you don’t need individual fan speed control in most builds. You are going to run all three fans on a radiator at the same speed, so it comes down to case layout and a little math. The logical arrangement with 10 would be all 6 radiator fans on the powered hub, which then has 1 PWM connector on the Com XT. Your remaining 4 fans connect directly to the Com XT and can be controlled individually. 
 
Since the case already has a powered PWM hub and you are very likely to wind up with at least one LNCore through purchasing fans, this saves you the cost of the Commander XT. When would you want two Com XTs instead?  If you need two LED channels. Each Commander XT has one. Assuming your cpu and gpu block are Corsair, they will daisy chain together with the XD5 and use 1 led port for all three. However, if you want to add strips or if your blocks are not Corsair, you are going to need a second LED port and the Com XT is one way to get that. 
 
5v load is going to be the same in either case. With the PWM hub it offloads power delivery from the controller to the SATA-> PSU directly, so that’s not an issue. 
 
One thing to keep in mind if you do Commander XT x 2 is each is a separate controller with its own 2 temp sensors. The standard arrangement is a single temp plug in the XD5 leading to control. You will want a second temp plug elsewhere in the system so both controllers can operate as you dictate with or without the CUE software running. Whether at a radiator port or as a T fitting, you connect another temp sensor so each Commander XT has its own data to run fan control. 

Not something reported very often.  Try deleting both GPUs from the dashboard, then quit CUE, the Corsair.Service 32bit, and Corsair CPUID service from the task manager (or just reboot the PC).  After CUE loads again, add the GPU back to the dashboard through normal means.  Hopefully that results in one GPU.  You likely will need to redo your Nexus widgets.  
 
If that does not work, try a repair install.  Go to the Windows Apps list and click on the drop down menu for Corsair iCUE.  Select "modify" and follow the prompts for a repair install.  This will not erase profiles or settings but will re-establish the connections with the OS and GPU driver where CUE gets that info.  Not sure on origin.  Could have been a one off error.  Maybe on a new GPU driver install done while CUE is running?

If the CPU is skipping up toward 90-100C in a visible fashion, then the pump is not running.  Shut down the PC and flip the PSU off.  Then disconnect the wide power cable from the pump to the side of the Commander Core and reconnect it making sure the white stripe is lined up.  Flip the PSU back on and boot up to the BIOS so you can see the CPU temp.  If you've just been in the BIOS and the CPU temp heated up to 80-100C, it will take it 30-60 minutes for the liquid trapped in the cooling finds to naturally lower in temperature.  If the pump is now working, that should happen in a few seconds.
 
You have lights so there is some degree of power.  However, that wide 20+ pin cable can be a bit finicky and there are multiple wires for power, 5v lighting, etc.  The power cycle also forces the controller to reset on the next power on.  If this does not work, contact Corsair Support as a means to replacement or do the same through the purchase vendor.
 
There is a specific defect some users encounter where the pump alarm incorrectly is triggered preventing you from accessing any device settings, even though CPU temps are normal.  That's not a user correctable issue, so fortunately that is not in play here.  

Murals is the replacement to "Instant Lighting" from CUE 3.  However, there is another way to set up one click total system color changes.  You can use the Lighting Link options to create individual profiles with specific lighting functions.  
 
Assuming you are using 1 "default" profile right now (the name does not matter), go to your profile list on the left side and click the three vertical dots to extend the pop out menu.  Select 'copy profile" and a duplicate "copy of default" will appear below.  Go to any of your devices and click + to add a lighting effect, then go to the bottom of the list where the Lighting Link presets sit.  You can choose from static, rainbow variants, and other lighting presets that will instantly be applied to all connected capable devices.  Then go back and rename the profile "static color" or "spiral rainbow" or whatever you prefer.  
 
The advantages of doing it this way is it should not lock you out of the motherboard and you can choose from more lighting effects than the murals system offers.  An additional benefit is you can set up profile switching for a Corsair KB or mouse to cycle through them or even easier is it will add all of these profiles you create to the task bar pop up.  Now to change the lighting you do not need to open CUE and adjust the murals setting.  You can choose freely from the all the profiles you create and change with a click. 
 

The AX860i is no longer in production and that is not what I would recommend for anyone at this point even if available.  "Best" is hard to quantify, other than reliability and the PSU's efficiency rating.  In the 850W size, the HX850 is the only Platinum certified PSU.  All the others are Gold.  However, that may not be a meaningful difference and other features may have more value.  I would keep an eye on the number of sockets available.  On a 850W it is possible to run out of 6 pin accessory slots in a systems with lots of stuff packed inside.  The other consideration is if you want/need an ATX 3.0 PSU.  You won't for your motherboard, but the presence of a direct 12vhpwr socket so you can do a direct run GPU->PSU may have value.  There are not many of those, so you will need to plan for a 12+4  -> 2/3 x8 PCI-E adapter for whatever PSU you buy.
 
You might also consider going up to 1000W.  I think 850W covers it , but at 1000W you get more sockets and a bit more breathing room.  It also opens up some other choices, including an "i" PSU that has additional levels of control and data in CUE.  
https://www.corsair.com/us/en/Categories/Products/Power-Supply-Units/HXi-Series-Fully-Modular-ATX-Power-Supplies/p/CP-9020214-NA
 

It suggests there is some type of electronics problem.  We could speculate about why, but if did a power cycle and rechecked cables, it went away and then came back again, that does not seem like a cables issue and is not likely something you can not correct on your end.  Contact Corsair Support through the link at the bottom of the page as means toward replacement.  

Temp 1 is the typical “gpu temp” everyone is accustomed to. Temps 2 and 3 are the “hotspot” and VRAM temps found on 3000 series GPUs. Programs like GPU-Z can help you identify them by matching temps. 

Is that an MSI x570?  Red is the 'default color' for a lot of systems and there the MSI motherboard 'Commander Center' or whatever it is called now often gets entangled with other components.  If you are running MSI commander center, Gigabyte Fusion, etc., try quitting that application and it's subroutines from the task manager, then quit and restart iCUE.  
 

Well, that’s the problem. There is a clear issue with some units that trigger a false pump fail. The pump is running and cpu temp as expected, but it locks out the Commander Core so you can’t use it as a fan controller or control RGB, so this not a workable condition.
 
Multiple users have swapped in new Commander Cores but it does not solve the issue. Whatever the source, it is hardware related and on the pump circuit end, not the tachometer cable itself.  Unfortunately replacement is the only solution, so hang on for support. Make sure you mention you’ve already tried it with another Commander Core. Recently another user mentioned support had sent him a new one to try, but we know that does not work for this ‘false pump fail’ problem.