The thing is.... (i don't know how true this is, but for some reason it works), since I assume that you edited the music_db.xml to add the songs and I also assume that you already put the corresponding files in the songs folder, then this may go interesthing, for some reason, the .s3v song files located in the folder, doesn't work when you try to play the song in the game, so then you need to have those files, but in the .2dx format instead. (i am not really sure if this is the actual solution, my theory is that the problem actually lies in the .vox files which would be the difficulties of the song, or it could also be that the .s3v files need some conversion so that they also work in the game, the truth is that I don't know, but this is what I think)