Congratulations for your MIDI Block!
That's something I also had in some time ago, but never found the time to do it.
Maybe you're interested in the following link: http://www.musicxml.org/xml.html
It seems to me that this is going to become *THE* standard for music data in XML format. There are many programs which already support this format (Finale, Sibelius, KGuitar, ...). This also made it possible to exchange music scores between Finale and Sibelius.
An important information for you might be that MusicXML also includes a representation for MIDI events.
Perhaps you're interested in a proposal of me (which actually was thought rather as Random Thought [RT]) where I already sketched some ideas for dynamically aggregating (mixing) music data and serializing it as binary sound, but have a look at it yourself:
http://marc.theaimsgroup.com/?l=xml-cocoon-dev&m=104482372430759&w=2
Keep up your good work!
Bye,
Andreas