I might actually use this. I was trying to write this for .NET 2.0 so that it would be compatible with running on Windows 98, but music is more important than comparability. If I use version 3.5 I can use the WebClient class to download the JS and the JavaScriptSerializer class to process the result. That does mean I still need some tracks, just in MIDI format. I'll look into implementing this today and get back to you all.
The engine will now load json files generated by the toneJS MIDI converter. I've posted the source on GitHub, with a debug build of the game that automatically loads and plays "music.json". The sound quality was pretty horrendous with the test MIDI I used, but it wasn't an 8-bit track, and was probably never meant to be played with just frequency and duration. Have a look and see if whatever music you're planning to produce for the jam will sound ok. I also want to say thanks to HeavyPixels for providing this great resource.
https://github.com/LucidaDragon/Ninja/tree/master/SmolGame/bin/Debug