hi,

6x r9 290 will take @stock voltage and non OC 2100W. (incl board, cpu and memory)

I use the asrock h61 pro btc without powered riser.

I have no problems. The Board is build for using x1 riser without molex.

Operating system is Win 8 (easy to setup and you can use afterburner)

cgminer and cgwatcher