I've got a brand new build and an updated install of 12.04. I was having trouble with installing Radeon drivers from the 'Additional Drivers' application, so I followed the directions here: http://wiki.cchtml.com/index.php/Ubuntu_Precise_Installation_Guide to download and install the drivers and Catalyst directly from AMD. Video works fine now, but I'm having no luck with audio. In the 'Sound Settings' dialog, I can't choose HDMI out as the output device. I also tried adding radeon.audio=1 as a boot parameter, but I'm still having no luck. Any ideas on how to get HDMI audio out?
Never mind, I've finally managed to get sound working! Because I hate when people say they got something working without saying how they did it, here's where I found my answer: No Sound card detected in Sound Settings, although sound works Not exactly my problem, but the sound card wasn't showing up, so I gave it a shot and, ta da! Sound through the HDMI port!