Problem with multichannel audio output on video file

Greetings,
I would like to use my RS150B to also watch music videos with multi-channel audio (Dolby digital - DTS).
To do this I tried to connect the hdmi output to my amplifier (I also tried the coax output). Unfortunately even if I select the correct audio output from the VIDEO app (vlc) (such as dolby digital) the signal ALWAYS comes out in STEREO…how can I fix it???
Please help me.

Thank you very much

@Hunter

In the default video state (VLC plug-in Off), you can use it after setting HDMI Passthrough On from the input/output settings.

Thank you