Exploitee.rs

Is there problem with dolby digital output on logitech revue?I have connected my AVR with digital out cable to my logitech revue and when I set audio output as dolby digital there is no sound comes out from LR rear (surround) speakers but when I change setting to PCM I can get special effect sound from those rear speakers which are supposed to come in 5.1 channel.
Is anybody observed same effect?If so can you tell me how to trouble shoot that problem?