As another proposec nomination, i nominate 'The Encounter'. I cant believed that you missed it out - it's the best boss music in KHII!

As for where you can listen to songs from the game easily, Kingdom Hearts OST Soundtrack Mp3s - Blue Laguna's Media Archive and Kingdom Hearts II OST Soundtrack Mp3s - Blue Laguna's Media Archive should do the trick.

As for nominating between the current two, i vote for Sora.