Don't beat around the bush try one of these PSU with 32 PCI-e cables and plugs. Enough for all of the cards and can plug straight into the risers which is better than any adapters.

http://www.parallelminer.com/product/rev2-ultimate-2400watt-power-supply-kit-for-gpu-mining-94-platinum-efficiency-200v240v-w-32pcie-plugs/

You would still need a small PSU to turn MB and HDD on and for the CPU power