Man you've been having bad luck with this stuff.
I had an Asrock extreme6 running 3 cards for a while. To eliminate any possibility of it being a board problem, try running the cards in the top 3 slots. One in the highest x1 slot, then the two in the closest x16 slots. Plug the monitor into the middle card, the card that is in the topmost x16 slot. That is what setup I had, so if yours don't work in those slots then we can focus just on drivers.
you noticed huh? lol everything was perfectly fine until i bought that fan from fry's lol. So I can get 2 7950s running in any configuration on any of the 3 slots now. I am unable to run 2 7950s and 1 7790 in any order. I'll try 3 7950s and see what happens. When I use a unpowered x16 riser cable on the third slot it shits out. I should be able to get a monitor signal from the last slot corrrect? The worst part is that I JUST HAD THIS WORKING. oh well.
I got some steps to try on the other "burnout" mobo from asrock support. He said I should still get monitor signal on a no input error.
It would be good to try just 7950's. Although, I had 2x7950's and 1 6950, which, in theory, should be more complicated than getting your 7xxx series cards to work together. As far as which cards can get a monitor signal, any of the x16's should be able to but I noticed I had issues when any card other than the one in the top slot were plugged in to a monitor.
Also, are you plugging in the extra molex power by the PCIe slots? You should do that just to be safe.
