If the VLC Audio channels do not work very well, you can simply open a ticket in the VLC error system.
If you can't wait to fix the problem, just redirect the audio output to STDOUT and use a tool like SOX to do the work for you.
Choosing a private channel using sox:
sox stereo.wav -c 1 mono.wav avg -l
Of course, sox can work with streams and not be limited to files.
BTW, sox comes with playback and recording utilities that can perform actual playback. see examples here
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