There's a local DVB-T channel that uses two audio tracks (MPEG and Dolby Digital, both stereo) - I cannot find a quick way to switch them in MC. Channel properties attached, only difference of the "AC3 version" is the audio PID (690).
If I manually change the APID and Audio Format to Dolby AC3 it seems to play the AC3 track although I'm not sure (Audio Path/Input only reports: 48 kHZ 32bit2 ch).