Digital Output and HD Channels Freesat

[Alucidnation]

Hi all,

Just hooked up an ageing Panasonic plasma tv with the digital optical out to my digital AV receiver, however, when i select the HD channels on the built in HD freesat tuner, the audio goes silent.

Am i missing something here?

Should i be looking further into the menus for an output setting on the TV?

Thanks