Working backwards, confused by voltage requirements.

Hey, I'm trying to get a new i5 system together and although I know my way around computers for the most part I'm getting a little frazzled n' I'm wondering if anybody could help with this little problem.

First off, I ordered a set of TW3X4G1600C9D mostly on impulse as it was on sale at a great price in very limited stock and it's close to exactly what I needed.

The motherboard I was planning on getting was an ASUS P7P55D LE, and it's not on the compatibility list so that's sort of out the window. I figured it was the low voltage on the DIMM slots, but the Gigabyte GA-P55M-GA4 is on the list and from reading up on it, it appears to have the same voltage on its slots.

I was just wondering either why the P7P55D isn't compatible and why the GA-P55M-GA4 is - or which LGA1156 motherboard might be a better choice, looking around the lower to mid-section of the boards out there.

Sorry if that's too much of a wall of text but I've been going over this for a little while in my head and it's really got me confused, thanks to anyone who can help. Also is this even in the right board? I figured it's to do with memory compatibility.