With the help of Rocco, we now have a pure Perl way to interact with XMMS using POE. This code will probably end up on the CPAN as POE::Component::XMMS (with POE::Filter::XMMS).
And I'll be using it in my djbot, since mpg123's playback just stinks terribly.
I've got a bit of work to do but it will be worth it.