I'm using Mythbuntu 8.10 on a board using the ALC888 codec, and I am wanting to use the SPDIF output as a digital pass through to my receiver so it can decode the AC3/DTS streams.

Using the "-ac hwdts,hwac3" switch in Mplayer seems to do the trick, and the DTS and dolby digital symbols show up on my receiver to indicate it is processing a digital audio stream. The problem however is that I only seem to be getting 2 channels instead of the 6"channels encoded into the audio streams. Looking at the output from Mplayer I noticed this;

Forced audio codec: hwdts
Opening audio decoder: [hwac3] AC3/DTS pass-through S/PDIF
No accelerated IMDCT transform found
hwac3: switched to DTS, 1536000 bps, 48000 Hz
AUDIO: 48000 Hz, 2 ch, ac3, 1536.0 kbit/100.00% (ratio: 192000->192000)
Selected audio codec: [hwdts] afm: hwac3 (DTS through S/PDIF)
I've also tried Xine with the same result, and even tried;
"speaker-test -Dplug:spdif -c6 -l1 -twav"
But only get audio through the front left and right speakers. I've tried adding "options snd-hda-intel model=6stack-dig" to the end of /etc/modprobe.d/alsa-base and have upgraded to ALSA 1.0.19 with no effect.

Any ideas/suggestions?