In Nomine Homebrew
This is just a partial listing, and completely ignores attunements and artifacts.
Attraction, Charm, Dreams, Entropy, Form, Harmony, Healing, Light, Motion, Numinous Corpus, Possession, Projection, Shields, Thunder, Tongues
And, from the Book of Songs, we get…
Affinity (Contagion), Artifacts, Cacophony, Calling, Darkness, Direction, Draining, Empathy,
Essence, Fire, Forbidding, Ice, Location, Machines, Memory, Might, Nemesis, Nightmares, Nimbus, Opening, Plagues, Revulsion, Sanctity, Seals, Sensation, Shadows, Sight, Silence, Sleep, Solace, Storms, Succor, Symphony, Transferal, Transfiguration, Truth, Unity
And that’s ignoring the secret songs… So, maybe we don’t really need to make the tracks any deeper or more expensive — it seems like there are so many useful ones that the players will spend a lot of xp on collecting them. So… maybe like Changeling Contracts, they could be 5 xp for the first version, 10 for the second, and 15 for the third?
If we create the secret songs, maybe they have prereqs like some of the Vampire Devotions.
My suggestion? First I’m not quite sure what these secret songs are but from the sound them may I recommend making them exclusively accessible through roleplaying. If these songs are secret, have the players investigate, research, and discover them.