Giving up now. Just sayin'
P.S. It turns out that this LJ FAQ page is in error. It currently says:
Your voice posts are automatically podcasted on your RSS feed:
There is no way to podcast other audio files through LiveJournal.
What it does not say (but which is obvious in retrospect, even if they should have made it explicit IMHO) is that only PUBLIC voice posts are automatically podcasted on your RSS feed. Even though they encourage you to put voice posts into a filter on the voice post settings page. *facepalm*