This info is not tested but was found here:
http://ptspts.blogspot.com/2009/08/asrock-ion-330-nettop-with-jaunty.html
HDMI and S/PDIF audio output
When diagnosing sound problems, make sure that pulseaudio is not running:sudo killall pulseaudio
Please
also make sure that no other program might be using the soundcard:
disable system sounds, kill all web browsers (to kill the flash
player), and kill all media players.
To get default audio output on the analog stereo jack, run$ mplayer -ao alsa $FILE
To force audio output on the analog stereo jack, run$ mplayer -ao alsa:device=front=NVidia $FILE
To force audio output on HDMI, run$ mplayer -ao alsa:device=hdmi=NVidia $FILE
To force output on S/PDIF, run$ mplayer -ao alsa:device=iec958=NVidia $FILE
To list all available audio output devices, run$ aplay -L
Please note than when specifying anything other than -ao alsa to MPlayer, you may lose DMIX support, so you won't be able to run two playbacks at the same time, and MPlayer would print:[AO_ALSA] Unable to set hw-parameters: Device or resource busy
It is possible to fix that by using plain -ao alsa and specifying the the output device in $HOME/.asourdrc. Using the environment variable ALSA_CARD does work, but ALSA_PCM_DEVICE doesn't seem to work. Set up your $HOME/.asoundrc like this:defaults.pcm.!card NVidia
defaults.ctl.!card NVidia
defaults.pcm.!device 0
defaults.ctl.!device 0
The device number 0 is analog output, 1 is S/PDIF and 3 is HDMI. The device numbers come from the output of aplay -l.
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