Why won't HDMI audio work with Radeon HD 7850?

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http://askubuntu.com – 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? (HowTos)