Surprised something as old as those are still under warranty or dell can still find them.
Still, even with just one card in it should display fine.
Looking at that extender and it would appear to only support single link dvi which is incapable of supporting the monitors res. Did you say you have been using that setup for 3 years?
Can you test it without the Gefen device?
I am thinking along the same line, going to test this evening ( a little heavy for my lightweight self - but the workout never hurts ) Thanks, I will let you know if Gefen is right or not.