You have different motherboards for AMD/Intel because the processors, the underlying transport technologies (HT/QPI/FSB/whatever) and the physical sockets are fundamentally different. With graphics cards, they all connect through standard PCI-E, so as long as you have one (you do if this is your sig computer we're talking about) it'll work (provided your PSU can give it enough power, which it should). The only time you should be concerned about the motherboard is, as Bootup said, when planning a SLI/Crossfire setup, in which case you'll need a compatible chipset. This has no bearing to ordinary multi-GPU setups where you get extra cards to support more monitors, however.