"Aight ChimiChanga that's all great but how do I actually use this?" - You presumably

This assumes you know the basics of setting up a folder in your addons and how to turn it into a VPK.

First get the actual music files you want and put them in the "sound" folder of your addon directory. Ensure that the music files are UNDER 48000Hz, are .wav files and have loop points set up.

Then create the file with this folder path in your addon directory -> "scripts/vscripts/director_base_addon.nut"
You could call the script differently as long as it isn't mapspawn_addon but the one above will fire automatically.

Now open the file in your text editor of choice, and now to actually set up playing the music. To add a track with a "calm" and "battle" variant put this in the script:

The "map" bit is the filename of the map to add the music to, setting it to "all_maps" will add the music to all maps.
The "calm" and "angry" bits correspond with the filenames of the "calm" and "battle" versions of the music to play.
The "consistent" bit is a true or false on whether to have the 2 sounds be synced. If set to true, the music will blend into each other at the same position in the track. Having at as false will pause the respective tracks when the other is playing

So say for example I wanted to add 2 consistent tracks located in the directory "sound/music/ultrakill/" for map 2 of Dead Center then I would write:
Make sure not to include "sound" at the start of the filename or else it won't work.

You can also just have 1 track play the whole time without changing like this:

Again, the "map" is for the map filename and "angry" is for the sound to play at all times.

Further functions for customisability are in the "Further Utility Functions" discussion.

And there you go, build a soundcache for your sounds and your music should play in the map you chose.