When switching HD channels my 921 looses audio. It is connected via Optical cable to a B&K AVR 307. Switching Surround Modes on the B&K (from Surround to THX) for example restores the audio. Changing channels to another HD channel on the 921 does NOT restore Audio. Changing channel to an SD station does restore audio. On the surface this might seem a B&K problem however it does not Happen with the SD channels. Nore did it happen with a Dish 721 reciever over 7 months. Also have tried 2 dvd and a cd player all hooked optically with no similar bugs.