This is a shot in the dark but... Has anyone got any change with this setup?
I can't seem to launch Ubuntu Live CD, either Trusty (14.04) or Saucy (13.10). Whenever I click Try Ubuntu it hangs and the screen flickers. The only way I could manage to do it was DISABLING the internal GPU, thus using only R7 discreet card, then the live cd would boot up completely and finish install.
But then, I switched driver to fglrx, enabled the internal GPU on the bios again, got the second monitor sort of working (it wasn't the wide desktop thing). When I rebooted after turning on Xinerama the system freezes after login. I can't neither open another terminal on CTRL+ALT+F1.
On recovery mode tried uninstalling, reconfiguring xserver, and installing fglrx 13.30 that I had downloaded previously, next boot it didn't reach the login window.
I think I'll try another round of installs tomorrow, and try to figure out how to activate the second monitor without Xinerama.