I would say take a look at the latest fglrx drivers at elrepo and see if they work.
Thanks for the suggestion but unfortunately not. When I boot a 6.6 kernel with the fglrx driver, my machine completely locks up. with the stock ATI driver X would lock but I could still ping/ssh to the machine. I can still boot using the fglrx driver with a 6.5 kernel (but performance seems worse than before...). Any other ideas?