WHAT DON'T WORK:
ASUS M4N75TD with PCIe Powered risers (in the 16x ports and in the 1x ports)
If I connect the molex, the motherboard doesn't even post.
If I did NOT connect the molex, the motherboard sometimes works, sometimes it doesn't start.
same behavior with 16 to 16x extenders that with 1x to 16x extenders.
tested with Sapphire 7950´s
this mobo doesn't like extenders WHAT WORKS:
Curious, the cheap Gigabyte 78LMT-S2 motherboard works with 2x 7950 using: 1x 16x to 16x powered riser, and 1x 1x to 16x powered riser.
Interesting option as this motherboard is really really cheap, and for 2x 7950 is not a bad choice!!
However, comparing it with the Gigabyte 970A-D3 the performance is lower.
What I mean, is that in widows 7, the second card (in the 1x connector) is about 80% load, not more, ever, and with the bigger mother 970A-D3 load is 99% in every slot, probably has to do with limited bandwidth of the 78LMT-S2 , dunno.