Strange SPDIF problems

[evilpenguin]

I'm having a pretty strange problem with my SPDIF output. I have a Shuttle SN25P with via ENVY-PT on board sound and i'm using the nVidia decoders set to pass though SPDIF ro my reciever.

I start up Sage (or MCE, they both do the same thing) and I load up a video with non-AC3 audio(reciever shows pro logic) and everything plays perfectly. Then I load up a video with AC3 audio and everything still plays perfect (reciever shows DD or DTS). However, now if I try and go back and play any video's with non-AC3 audio I get absolutely no sound (reciever show pro logic), but anything with AC3 audio still plays normally. Sleeping Sage and reloading the media player does nothing. To get back the non-AC3 audio I need to completely restart Sage.

I can however, load up the videos in the same order in windows media player or VLC and everything will work fine.

Basically i'm wondering if...
1 - Do Other people with ENVY drivers (4.73b) have the same problem?
2 - Are the ENVY drivers good and is Sage being bad or vice versa?
3 - Could it be nvidia's audio decoder, and if so what are my other digital options, assuming I don't want to give up being able to play DD and DTS on reciever?
4 - If all else fails, does anyone know of any good usb sound cards that will do what I need to do perfectly?