thomson dpl 550ht - no sound trough optics

hi. i am trying to setup a thomson dpl 550ht sound system at a friend. the analogue input works fine as well as the radio.
unfortunately when trying to play via optics: tv -> receiver i have a no sound issue.

Any idea why this does not play? I tried manuals an everything but nothing helps.

Is there a way to reset this device? could not find the correct steps.

Please help!

ps: i have no remote.





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