I just got sound over hdmi working last night. I just had to pass the
right model to the sound driver. [3]
[1] https://bugzilla.redhat.com/show_bug.cgi?id=496772
[2] http://bugs.freedesktop.org/show_bug.cgi?id=11220
[3] https://bugzilla.redhat.com/show_bug.cgi?id=502890