Yep I bet that's the prob... I'm using one of these
. There are a few other options on the Egg that are a little cheaper now and probably work just as well. Combine that with something like this
and you should be good to go.
Let us know if you get it working, Eyefinity is going to be sick on those screens, I thought three 24" screens were cool. You may also find that you'll want to pop a second 6950 in there down the road, but YMMV.