You can't do Quad-SLI.
Anyways if you knew the answer then why bother posting? I also don't get maxi-heads that want the max, I doubt you'll be able to even see 2xAA at 2560x1600, I finally don't know why people want such huge monitors, even ASUS's 25.5 inch 1920x1200 is pretty big, and if you're going to sit far away you might as well as get a big TV.