Reinstalled the 10.6 drivers and now it seems to be working correctly. If I come across any more problems, I'll post again, but for now, my problem is solved.
One thing that DOES concern me, though, is that now when I look at GPU-Z, for BOTH cards it says it uses the same BIOS version of the cards. Before, it detected both cards but displayed a different BIOS version for each card. Should I be concerned about this?