I'm running this chip with unstable and it boots fine.
Looks like testing and unstable are on the same X.org currently, but unstable is using a newer kernel.
Also I see something in dmesg about kaveri firmware being loaded, which I believe is provided by the
linux-firmware-nonfree package, in case you don't have this installed.
Looks like Petter has a better handle on this stuff than I do, so follow his instructions for getting
the system to boot to the command line.
Later, Seeker