I also have an ASUS A7N8x-E Deluxe Revision 2 board and am having this EXACT same problem. The strange thing is, I have my SPIDF output hooked up to a DolbyDigital amplifier and when I use the nforce-audio module the reciever lights up in DolbyDigital mode jsut like it does in Windows, so evidently it is getting a Dolby encouded stream. I just cant get any sound no matter what I try.
One other thing I get is when I try to pipe a wav file to /dev/sound/dsp using cat, I get an error say "Illegal seek"
WTF is up with that?