It shouldn't be too hard, in theory, it'd just require a lot of time, and a lot of typing 
You want to go have a look at EB/Data/descr_sounds_music.txt
Inside, you'll see all of the music split up by different factions and different factors which decide which song to play.
Then you'll want to go to your Vanilla backup (or 1.5 patched or whatever) and find the same folder.
The first bit-
-should be the same in both, if it isn't for some reason, use your common sense and decide which one is more practical.
Now, in your vanilla backup, head to Data/Sounds/Music
For me, it got a little complicated. Instead of folders, I had a combination of .dat and .idx files, so Music.dat and Music.idx. If this happens to you, you'll probably want to go to this site to make it normal and access the files inside.
I didn't actually do that because I'm too lazy
, but i'd assume inside you'll find a bunch of mp3s with names like Death_Approaches.mp3.
Copypasta these files into your EB/Data/Sounds/Music folder (AFTER MAKING A BACKUP!!), if you want create a subfolder initially so all of the songs don't get all mixed up.
Then, now here's the fun part
, you need to transfer the links from your Vanilla descr_sounds_music.txt into your EB descr_sounds_music.txt into the right places (AFTER MAKING A BACKUP!!).
For instance, you'll want to make sure that you're taking the song locations from the ROMAN MUSIC section into the ROMAN MUSIC section of the EB file.
Etc etc. The only thing i'd be wary about is changing the startup game music. If you change this, make sure there's only one song, eg
not
because otherwise it might mess the game up.
It's pretty simple stuff really, i'm not a modder but in theory this should work easy.
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