I browsed through my F2k files and in the folder fifa2000/data/audio/music, I found the some music files. They're named fifa0000.str to fifa0007.str. In the same folder I also found an .inf file called music.inf
Inside the file only fifa0000.str to fifa0004 are written. I started to do some editing by adding the missing files, but when I started the game it crashed. I had to install the game again to make it work.
What did I do wrong? Had I do a computer restart before starting the game or is there something wrong with my editing?

I'd appreciate any input from you about this issue

It is a curious thing. I have the Spanish version of the Fifa 2000 and my music.inf includes all the files from 0000 to 0007. I have tried to edit it to be able to listen more songs (just rename asf files from Fifa99 to.str files) but the new songs don't play unless I delete one of the original ones(the game no crash). But I listen the 8 original songs perfectly. I think that eight is the maximum of songs supported by the game. Try to edit music.inf with a good hex editor (hex workshop,.... )

Thanks for your input. I'll try some more editing.

Nonetheless, if someone else has some useful input I'll still appreciate it!