yes that actually solved the problem.

i ended up cancelling that order and making my own powered risers out of normal risers like this: https://bitcointalk.org/index.php?topic=76121.0

way cheaper.

on my rig everything is running on the same 1600w PSU but if you have two PSUs it doesn't really matter what's where. Think of it like a power plug, it doesn't care what's connected to it. Just don't put too much on one...