Asus Xonar HDAV 1.3 - Manual (Page 100)

4 ASUS Xonar HDAV .3
Q8: Will PCM sound output through S/PDIF be just 2 channels even with
different analog output channels?
Answer:
The S/PDIF protocol specification (IEC-605) can only carry 2-channel PCM
data or non-PCM AC3/DTS data. So, when a user selects PCM output for S/PDIF,
the Xonar sound card will always deliver 2 channel PCM data through the S/PDIF
output port. For attaining 5. channel surround sounds, you can select Dolby
Digital Live or DTS Interactive encoding output from the S/PDIF out menu, which
will allow the Xonar HDAV .3 to deliver 5. surround sound for games, DVD
movies, and even stereo music.