I'd like to go the PSU route, but stuck with this EVGA 1000w P2 until I can upgrade.
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So I think for providing power to the cards - a 6-pin to 6+2 cable is the answer - then I can get the extra power cables.
The remaining issue is how to get power to all the Risers. If the PERF (peripherals) output on the PS will power a riser, then I have 4 SATA and 2 PERF.

Is there any reason to believe that 2 SATA to MOLEX cables can't run from one SATA cable to PS?
Then I can run two PCI-E risers off of 1 SATA PS connection.