Please update to the most recent pluto-boot-scripts
run /usr/pluto/bin/SetupAudioVideo.sh
Open the frontend setup (not backend) and change audio output to "ALSA:default" under "General",
and tell me if http://svn.linuxmce.org/trac.cgi/ticket/1295 "HD PVR audio port not being propagated properly." is resolved by this, and if not what the result is.