Tried on my own as well, alternative Mesa & Xorg stack booted okay with
provided 3.5 kernel or Jason's current 3.9.2 if you want. The problem was
elsewhere, first I thought it made use of LLVM-pipe CPU rendering back-end or
so, but then I realized that incorrect resolution [only up to 1280x1024
(5:4)] appeared there in options because of VESA driver used as opposed to
Radeon KMS-one.
Still I am aware of the mess with tainted firmware in case of any decent
AMD/ATi chip.. RS880's onboard HD4250 in this specific HW build.
Just did rollback any changes with ease.