Re: Dual PSU GPU Mining issues - Anyone doing this successfully?
It might not be your solution but at the very least you should be only using powered USB risers exclusively.
I am using two USB powered risers for two of my cards. The other two are powered by the mobo, which I figure is fine as it's a gaming motherboard (Gigabyte G1 Sniper A88X). Here is a picture of my rig (w/ two unplugged cards, was testing other two):
http://i67.tinypic.com/245lj6t.jpg
Try to add some old HDD to the 2nd PSU, so it will draw power no matter what happens with the GPU. It worked for me. 
I just tried this with a Blu-Ray drive and a HDD, but nothing changes. Thanks anyway.
Update:
More Pictures of My setup (fully connected and with HDD and blu-ray)
http://i66.tinypic.com/kaiuit.jpg
http://i64.tinypic.com/4uc9ia.jpg
http://i67.tinypic.com/2itg8zc.jpg
