I edited this on my previous reply while you were replying, not sure if you noticed:

Oh, one more thing... On the Asrock 13 gpu board, the PCIe slots on the board are so close, the small riser boards that plug to the motherboard might be touching each other and create short circuits. What I did is: I cut the excessive lenght of the soldered pins of the USB connector on the back side of that small board; used heat-shrink tube (1.5 inch wide) and wrapped the small boards where they could touch eachother, making sure the pins that plug to the PCIe slots are not covered. I would suggest that everyone usung the Asrock 13 GPU board do this to prevent problems... the heat-shrink tube is about 5-6 bucks and it's quete long, I don't remember exactly but it was at least 4 feet long. I got it from Sayal in Toronto but I am sure you can find one in electronic shops or even Home Depot.