This is the case when days can pass without a solution if you don't take the lead. I suggest one of you do it.
Make a temp partition and install a clean 8.1 from the new GA ISO. Don't bother activating, don't even use your key. Use the generic key instead or a gvlk. Once you're in the temp 8.1, install all updates, then reboot, then install Catalyst 13.11. See if your displays work.
If they do, you know what to do, reinstall your main system properly and you'll be good to go. If it doesn't work even in the new system, you'd better off sending a bug report for both AMD and M$. The former uses the so-called issue reporting form for this. You can read about it in the stickies.
CPU: AMD Phenom II X4 810 @ 3120MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 835/1135MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 3.11 Pro x64