Total Audio Loss on Sony HD300

I have had recurring problems with the audio on my Sony HD300. THIS IS NOT THE SAME PROBLEM AS THE INTERMITTENT DROPOUTS THAT HAVE BEEN CHRONICLED IN PAST THREADS. What happens is that the audio will suddenly disappear, sometimes randomly, but usually when the unit is turned off and then powered back on. The audio cannot be restored by the standard plug out/in method, but can periodically and randomly be restored with random pushes on buttons on the unit and every once in awhile by resetting the NVRAM in the service menu. I have changed connections, cables, etc, etc. I do not have any problems with my 2 HD Tivo units, nor my Sat T60. Sony has already replaced this unit 3 times. Every time the unit works fine for a day or so, and then fails. I did note that when firmware upgrade 2.01 came through, the audio was restored...until the unit was powered off again. Then no audio.

PLEASE HELP. Am I missing something obvious or do I just need to replace the unit with something else. I have both optical and RCA audio hookups to my Lexicon MC8B and neither of them will show audio. When I removed these units from the theatre into another system. they still had no audio. Any suggestions for troubleshooting would be greatly appreciated. Thanks in advance.