Also, the digital out is not stereo. It actually only outputs what it is told to output.
Therefore, if you are outputting, say, an MP3 or a WAV file, it will only output stereo.
If you are outputting a 5.1 DVD or video game, then the output will be in surround.
The NFORCE APU, on the other hand, converts all sound to 5.1 and "creates" the LFE and surround channels from the frequencies of the wave. This means that you can listen to WAV, MP3, etc., in an "emulated" 5.1 in addition to listening to 5.1 in true 5.1.