spdif output from mplayer?

[Tom Horsley]

I'm already overloaded with conflicting advice from web searches,
but since none of it has actually worked, I thought I'd try
asking here :-).

FC5, x86_64, mplayer (from livna), and a Biostar TForce4U motherboard
with onboard nvidia nforce4 sound.

The motherboard has an SPDIF output, and I can, in fact, get sound
from it when I run various games and wot-not.

But none of the things I've tried in mplayer have yet resulted
in the DVD sound being passed through to the SPDIF output
(I can only get sound on the stereo line-out).

Anyone with an nforce4 motherboard had success with mplayer
spdif out on Fedora Core 5?