There's currently talk on the LilyPond list about improving the MIDI
output. As LilyPond is an output format for some score editors and
we've been working on full microtonal support (I promise to get back
to this) it's an application we can target for high quality printed
scores. Maybe it could also give us the best quality MIDI output. At
least, anybody interested in this can have a look at that discussion.
The code's in scheme.
This is, I think, the only public message:
http://lists.gnu.org/archive/html/lilypond-devel/2008-08/msg00053.html
Getting a high quality performance from a score format is a very
difficult problem. It's work I'd prefer not to duplicate.
Graham