I have the exact same issue but with Asrock B550M board and Relatek divers/Nahimic app. I cant output from my 5.1 surround system unless the audio source is a 5.1 one, and the Speaker Fill feature vanished somehwere. Only work around I have found is to use a 3rd party Audio mixer called Voice Meeter but its not super practical thanks so much More @Wikipedia
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