you will need to be root for the following.
you have to edit your grub config. open /etc/default/grub
with your preferred text editor and look for GRUB_CMDLINE_LINUX_DEFAULT
and add radeon.audio=1
to the end of it.
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
becomes
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.audio=1"
now save the file and run update-grub
you may also want to try to add this parameters at boot time to ensure it works before doing all of the above.
after you power on you may need to hold Shift to get the grub menu to appear after it appears press e and add radeon.audio=1
to the end of a line similar to this
linux /boot/vmlinuz-2.6.38-8-server root=UUID=11111 ro quiet splash
becomes
linux /boot/vmlinuz-2.6.38-8-server root=UUID=11111 ro quiet splash radeon.audio=1
and press b to boot with the added parameter