Any luck? Exact same thing happened to me and I'm wondering if USB Risers are faulty.

I was using regular powered risers and it was working fine. I switched one of the cards to USB Powered Risers and it doesn't work. I've tried 2 different USB powered risers with same result. Card  is not detected.

I've tried in Asrock 970 Extreme4 and Asrock H61 Pro BTC

Asrock 970 doesn't have any Gen1 setting in BIOS as far as I can tell.