I am not familiar with the game. Does it use CDA tracks for the music?

The game originally plays from CD, requiring an audio cable. You will probably want to make an ISO and mount it, and if it gives you trouble still, set the virtual drive as d:\

Isn't there a gigantic library of mods available for this game? I would expect one of them would let you do whatever you wanted to the music.

It does have CDA but it also has midi as a fall back.
You can force midi by adding "-midimusic" including the quotes after at the end so the shortcut would look something like
"c:\games\aoe2.exe"-midimusic""

(I cant remember off top of my head what the exe is called)