The instructions for nforce4 at the bottom of: http://alsa.opensrc.org/index.php?page=intel8x0 actually seem to work! I can get 5.1 audio fed to my receiver now over the spdif output when playing dvds with mplayer. There were only about 47,321 totally conflicting web pages with different instructions for doing digital pass-through. But, its all worth it to get mplayer to go directly to the $#@! movie, skipping all the promos, FBI warnings, and interminable menus :-).
