Comment 6 for bug 1511429

Unfortunately fglrx does not support RandR 1.4. The only solution, in your case, would be to use multiple xscreens which I think Kubuntu supports but Ubuntu doesn't (because of Compiz). Unfortunately we do not support this use case. If you do decide to go down this path, you will probably want to disable gpu-manager by passing "nogpumanager" on boot.

The other alternative is to use the open source drivers.