we really need a clear answer of this question. Hopefully some one can get it tested real soon.
I did test it, the system wouldn't boot any OS with 3 cards (and thus 6 GPUs) installed. I only tested x86 OS's, however.
try a 64bit os and will it even post as in you can get to boises and stuff? you might be running out of bios address space try to disable every thing you don't need might just give you enough free space to boot