My HTPC has the desktop off the top of the TV and frequently the HDMI audio doesn't work.
With my ATI graphics card on my desktop I have a script that runs on startup to force the display drive to to detect my 1920x1080 monitor otherwise it displays the screen with big black bars all around the edges.
Proprietary driver I assume? That always has been, and always will be (as far as my crystal ball permits me to see), a clusterfuck. If you opt-in to that sort of pain, don't act surprised when you receive pain.
With my ATI graphics card on my desktop I have a script that runs on startup to force the display drive to to detect my 1920x1080 monitor otherwise it displays the screen with big black bars all around the edges.
Audio and video are still a pita for me.