Erm... it won't work... it not supposed to work like that i am afraid, you are confusing the motherboard. The way to egt two graphics cards in is via SLI or crossfire, and then they have to or should be teh same model and same connector type.
I am certainly not an expert on this, but from all the reading I've done, SLI and Crossfire are meant to use multiple GPUs to improve performance on a single display. That's not what I want to do.
I want to have multiple displays. I have 2 monitors right now and want to add a third. As far as I can tell, everyone agrees that to do that you simply add a second video card. There are warnings about driver incompatibilities and whatnot, but I haven't even gotten to the operating system yet.