Would this be a bad time to mention that Matrox TH2Go's will work on
each head of any of the 5xxx-series?
It's not official, nor supported (so don't ask them), but I'm on the inside and successfully got a regular 5870 to run 9 monitors with three TH2Go's.
I have a crappy vid of it, but need to edit out the audio, lol.