I reported this in the hdmi not working thread but after more testing i really do not think it is the same problem.
I have done a clean install of Mythbuntu 11.10 several times in the past week regarding this issue. I run mythbuntu 11.10 on this test machine, Vanilla included kernel. GT430, Asrock Z68USB3 board (no new bios file available) Myth setup is frontend only. I have Lcdproc, lirc, lm-sensors and xbmc built from git installed currently. I have alsa tested this with 3.3rc1 and rc2 both react the same way.
my /etc/modprobe.d/sound.conf includes
options snd-hda-intel enable_msi=0 probe_mask=0x108
So after installing x-swat and nvidia-current (290.10) everything works as it should I boot up check dmesg there is one instance of a hdmi hotplug. open xbmc and everything works as it should gui sounds, file playback is fine with all codecs. mythfrontend responds as it should live tv and recorded shows are fine.
After purging nvidia-current and blacklisting nouveau and if I install either 295.09 or 295.17, drivers install fine, I reboot and it loads fine with my xorg.conf file. Open xbmc gui sounds are good so it initilaized the sound card fine, as soon as I start to play any file video or audio it looses the sound card and gives me a cannot initialize sound card, this is in the same session of xbmc. If I then exit xbmc and look at dmesg I see as many as 4 hdmi/dp hot plug instances all for the same eld valid and same monitor but I only have one instance of the sound card in alsa as per my sound.conf probe_mask dev 7, 8, 9 are masked and only dev 3 is active.
I included dmesg pastebins in the hdmi not working thread for both nvidia-current and 295 installation so a working and non-working report.
working 290.10 http://pastebin.ca/2113498
non-working 295.xx http://pastebin.ca/2113474