[japga]

1. Install xfce4-mixer in Ubuntu (Maverick)
2. Start xfce4-mixer in Terminal (by typing xfce4-mixer in Terminal)
3. Choose Elements ("Elemente auswählen"->i am on a german gui)
4. Activate "IEC958 1"
5. Close and activate "IEC958 1" again on "Schalter"


Now audio works on HDMI.

Found the solution here:
http://evilandi666.de/2010/10/mal-wieder...tu-update/

This is the easiest way without editing anything (at least for me)
HAVE FUN