Well I figured out the simplest way to fix my audio issue after a clean boot; after a while reinstalling (on command-line using dpkg with --reinstall option) the decoders-support package on every boot, I extracted the debian package and looked at the pre/post install scripts.

Turns out that a mafw start command fixes it, so something isn't running or is dieing that shouldn't be, just at/after system boot.
So now I have a simple command that lets gpodder start and the builtin audio player to work, so as root/via su or sudo I run (in a terminal):

/usr/bin/mafw.sh start mafw-gst-renderer

I don't know why this dies on boot or isn't started - it seems to run fine after I start it, I never need to do it again until the next reboot. So hard to find/trace the process that would normally start it at boot though! Anyone know anything?