Comment 4 for bug 989671

Just to make a follow up:

I just found in http://lucasromerodb.blogspot.mx/2012/04/sin-salida-de-sonido-hdmi-en-ubuntu-ati.html something that works for this system:
1.Do
$ gksu gedit /etc/default/grub

2.find the line
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

3. change to
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.audio=1"

4. do
$ sudo update-grub

5. Reboot

In this system (lspci gives Audio device: Advanced Micro Devices [AMD] nee ATI RS880 HDMI Audio [Radeon HD 4200 Series]), past versions of Ubuntu worked just fine, so I was confident that a solution was somewhere. However, this solution is not something that a complete newbie could do.