If I could suggest someting to eveyone , I'll say that TH2G can't be used on two outputs , and it can't be used for resolution bigger then 3x 800x600 on a single output .

Btw if you consider the cost of catalyst per output you save money anyway .

I've pesonally test a :

NVIDIA GeForce 7300 GT 256MB (DVI single-link/DVI dual-link)

on a Mac pro

and I was able to run 6 x 800 x 600 .

I 've test a g5 ( don't remember GPU model , it's the standard HES )

I was not able to use two TH2G .
also if I set the TH2G to 3x 1024x768 catalyst can't run , ( send to full screen remain all black , I think this is all about openGL stuff . )
Mac osX was able to see 3x 1280x1024 , but once lunch cat at full screen nothing happen . same for 3x 1024x768 .