I plan on updating the audio code in Sphere so that all file format decoding is done by the engine and not audio plugins. This would make the audio code more portable across platforms, but, if I can't find a good (and small) software MIDI decoder, I will remove MIDI support from the engine. However, it is very easy to convert MIDI to OGG or MP3 (see TiMidity++) or XM (see GMID2MOD). If you have any questions or comments, please either e-mail me or talk to me on IRC.