Alex, I replaced all the music in all the games with period stuff for the appropriate side. All you have to do is take the MP3's run them through a convertor to .OGG format, rename them as the originals were named and dump them in the directories.
You can grab a free converter here:
http://www.koyotesoft.com/indexEn.html
Also found as a bit of a bonus that what ever music you put as the xbackg1.ogg will also replace the intro music. So now if you like you can boot up East Front to strains of Panzerleid
Don't forget to back up your originals to another directory too.
Gary