Well the title says it all: ogg-vorbis format is currently not supported since pyvorbis is not ported to python3 and I strongly doubt it will be ...
Looking around I've found this package: PyOgg. It even supports FLAC :)
I've started already to see if I could replace the current ogg-vorbis handling with this new package but my capabilities are (again :-/) too limited. Before I spend too much time trying I'd like to hear from other more capable minds if that's a realistic plan ...