No passthrough for Dolby TrueHD

Hi,

I have a few BluRay rips with Dolby TrueHD audio tracks.  I noticed that 
Xine will refuse to play such track, and after some troubleshooting 
found out that it's trying to open an ALSA device called 
plug:surround51:0.  This is the default setting but it's invalid on my 
systems since I have only ever listened to surround sound through my 
home theater A/V receiver and have always used digital passthrough with 
it.  It looks like TrueHD gets handled by the ffmpeg_audio_dec plugin 
which does not support passthrough.

Would this be possible to implement?  I'm at a bit of a loss about where 
to start.  The ffmpeg plugin handles a whole lot of different formats, 
not all of which are appropriate for passthrough.  I also don't know how 
to wrap the TrueHD data; The AC3 and DTS plugins wrap the data with an 
S/PDIF header, but I couldn't find the appropriate values to use for TrueHD.

-- 
Mikko