I use a stand alone Dolby Digital decoder to hook my TV up to my amplifier.
When there is a 2 channel LPCM stream it works perfectly but when there is a Dolby Digital stream the sound comes to the amplifier in bits and pieces. Sometimes you get 5 seconds of sound and then it is quiet for about ten seconds and then you get half a second of sound, etc.
I have confirmed that it is not the decoder because when I hook my DVD player up to the decoder it works perfectly and the same goes for my satellite receiver.

The decoder correctly detects that there is a Dolby Digital stream but for some reason the TV does not work correctly.

The decoder is a Creative Extigy which does a perfect job in decoding Dolby Digital.
The DVD player is a Pioneer DV-600AV and the satellite receiver is a Dream Multimedia DM7025+.