They have 4 connections. Two have 2 x 8 pin, and two have 1 x 8 pin. They power the pci connections. For the risers, they're sata type, powered in pairs.
I think I've managed to solve the problem. I swapped the GPU distribution around to 5+1 (580/560) per PSU. Mining for 8 hours on claymore ethash and no problems so far. 328Mhs with 710W per PSU. Seems about right?
Oh yeah, that's good, let's waiting at least for next 24 hours. When you are using SATA connector for a riser power, make sure max one riser/rail, safer. Better using Molex (directly from PSU).