I've been able to pass the PCM audio out of my onboard sound card ( A7V8X-X Via8235 Sound) to the digital out of the MB.

I've been experimenting trying to pass through AC3 feeds from Mplayer and Xine for video files and DVD's.

When I add the Mplayer -ao hwac3 to the Myth player settings, I get popping noise ie. ones and zeros out, but the stream is not recognised as AC3

When I change ~/.xine/config to audio.a52_pass_through:1, I get the same result as above - popping

So it would seem to me the streams are passed to the sound card correctly, but they are not output correctly by the sound card...

which direction should I be heading to fix this?

note: I have no asound.conf at all

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Config:
ASUS A7V8X-X
ASUS FX5200 Magic 128MB
AMD Sempron 2400
256 mb ddr @333
120gb Maxtor HDD for system, recordings
250gb Maxtor HDD for music, videos
PVR-350 in "250" mode
PVR-250 "type 47" + IR unit
CD Rom