Game.musicdata is just a basic list of what non-race-specific tracks are in the Sound folder.
It goes by moods so there are MUSIC_QUIET, MUSIC_TROUBLE, MUSIC_UPBEAT, MUSIC_BATTLE, and MUSIC_SAD tracks. Each track has a different name such as Sad 1, Battle 5, Quiet 6, and you get the idea.
From what I can tell from the player files, each race has specific battle musics as well as other race-specific musics. This is where you would insert the specific music for each race.
The main menu music is known as Opening Theme.ogg. This is hardcoded (I think), and I am glad it is. You can make a different main menu music, it just has to be named Opening Theme.ogg.
All of these music files go in your mod's Sound folder. No, you don't need the rest of the Sins music tracks in there too. Only GameInfo is like that.
P.S. Its SpardaSon21. Please get it right next time. I really hate it when people mess that up.