Don't think it is a matter of "HOW".
Think it's more of . Thats what the program reverts to? Untill nVidea release drivers and Devs allow SLI.
That is what you have.
You are stuck between Dual core cards and 2X Vram cards.
You chose the former
2x3GB 580 cards would have been "The way to go".
Supposing they get SLI sorted. Garummpphhh!
