One of my HDR's seems to have lost the multi-channel sound output via optical cable to my amp. If I change the Digital Audio Output to Stereo, the sound returns, but is only flagged as Stereo. If I change it back to Multi-channel, the sound goes again. The sound output via HDMI to my TV still works with the HDR set to Multi-channel, or Stereo. I have rebooted the HDR, and powered it off via the rear switch, this has made no difference. I have power cycled my amp as well, also making no difference.