I have an A8 apu with 6620G and a HD 6750M, I have a custom bios that allows me to actively change graphics adapters on the fly. But to install fglrx I had to make sure I booted using the 6750M, then install, run "aticonfig --initial -f", reboot, and THEN switch to the apu graphics (6620G). The install will fail if you are using the apu graphics (powersaving) so you have to make sure you're using the discrete card, at least that was the case for me. Hope this helps.
