I had to do a couple of things to get the SPDIF to work from my laptop
to an amplifier. The ac97.c module that handles SPDIF did not have SPDIF
turned
on by default. My laptop disk just crashed, and I lost the patch to do
this, but it was minor, so if I get around to figuring it out again,
I can post that. If your system does not use ac97 then of course
this would not apply. Also SPDIF is expected to work at 48Khz, so
to get other frequencies provided by say xmms, I used esound(esd) set
at 48Khz, but can take any input frequency and do the conversion on the
fly.