Because finding and discerning current, accurate VLC command line usages is crazy difficult, a basic:
/Applications/VLC.app/Contents/MacOS/VLC <file>.mp4 :quit \
--sout "#es{access=file}" --sout-all
So far not successful at using VLC to downsample a 5.1 aac audio track to stereo.
Was successful with convoluted adobe audition workflow, but yet to remux.