well firstly i would like to say this IS indeed a plug in from bukkit, not a mod, and it could well indeed prevent lag from note block music by compressing the songs into boxes by music type (piano, bass, etc.). it is alos a type of thing that the song recorded to the note blocks activated by 1 redstone pulse. here's the link to the plug-in if you would like more info as well as a link to a video showing an example of it.

plug in url...
http://forums.bukkit.org/threads/fun-mech-musiccraft-v1-4-4-compose-music-play-it-with-note-blocks-1185.6705/

video link...
http://www.youtube.com/watch?v=CO6Jc7TdXmQ#ws