A bit confused...

Do you plan to use 2 GFX cards? I don't think there is a combo that would work that way in an X5000 as one card has to something that is not a Radeon.
Also AFAIK the builtin screen switcher won't work on such a setup.

If you plan to use 2 monitors on 1 GFX card it should work but I don't know which PCIe cards are supported for a setup.