Here's a super-close-up view of the PWM repeater. It's mounted with 3 screws to the back and it has SATA power and PWM inputs.
The chip in the middle appears to be a line driver, probably to make sure that all fans get a good signal. If you look closely on the SATA power connection (on the right), you may see that the 5V rail is connected - this actually goes to that semiconductor (via C2). The PWM input is connected to it (via R2) and the PWM for all of the fan ports is also connected to it. The tach (for feedback to the Commander Core XT) is connected directly to the fan on Fan 1.
This will definitely be useful.