Similar situation. Running crossfire and updated this morning to 12.8 (was at 12.3) and now my computer is doing 2 things.
amd driver stopped and recovering and at other times (as i can tell) kicking me out of WoW.
would love to revert to 12.3 but that isnt going to solve it.
so even changing the TdrLevel registry didn't help? You would have to find the driver path for both devices and enter in regedit.
do you have the CCC application profiles installed for crossfire. If you're not sure launch the CCC driver and instead of express install (which by default does NOT install app profiles) choose custom install and select the application profiles as well.
can you also try changing AA/AF settings (to OFF) in WOW to see if it stops crashing.
i have this problem too and i couldnt send ticket because it seems the ticket page is bugged and i know here is for developers..BUT cant you help people i m desperate here to solve the issue