Bug 1423 describing the incompatibility between Catalyst driver 9.1 and Xorg X Server 1.6 was posted back at the end of January:
http://ati.cchtml.com/show_bug.cgi?id=1423
It appears that "pciNumBuses" was removed from X with the release of 1.6 as documented at:
http://lists.freedesktop.org/archives/xorg-announce/2008-November/000696.html
The current Catalyst 9.3 drivers are still incompatible with X 1.6. This is now an acute problem for users of Debian Sid as X 1.6 has been rolled out.