I had the same problem. Optical spdif on ASUS A8N-SLI Deluxe.
The information from fpikus together with last post in
And i got it to work.
Some clues if you use kde like me:
Get visible light on the optical. Then at least the output is active.
You should see the IEC958 Playback AC97-SPSA slider in kmix. Set it to "All the way down"=0=Off (If you turn the volume up on the slider the sound turns off !?!) Its the same thing as fpikus says about value=0 in asound.state)
In the third TAB in kmix (I dont know the name in english, i have swedish KDE, maybe "Switches") you should see a selector for IEC958, set it to PCM.
Only 48 khz works. So
mplayer -ao alsa:device=hw=0,2 -srate 48000 <file>
Set arts to use OSS and lock it on 48 khz.