Xbox 360 connected to TV input HDMI4: Menu on TV: Sound > Additional Settings > SPDIF Output > Audio Format Drop down contains "PCM" and "Dolby Digital", however "Dolby Digital" is greyed out, i.e. cannot be selected. I have my V+ box connected to TV input HDMI3 and I am able to select Dolby Digital. Xbox audio settings is set to Dolby Digital. I know I could get an optical link directly from the xbox to the AMP however I'm curious to understand why I can't select this option on the TV. Thanks for any assistance.