Any help from people with this MB would be great. I've got the cable to hook up the 3rd card to the 1x PCI slot (the other 2 are in the 16x slots). When I take out on of the cards in the 16x slot, the card in the 1x slot works fine. So I know that each PCI slot works, they just won't all work at once.
In other words (somewhat redundant, I know, but) this is also what my brother tried:
I connected the card to the PCI express slot, and tried it with both no additional power and with additional power from GPU power adapters on the card. In linux I could only see 2 cards. I verified that the adapter works, by removing one of the PCI 2.0 cards, and the PCI express card worked at normal capacity.
In Windows I had dummy plugs, and I set up monitors for the cards. I could never get it to work right either.