Thanks for putting up with my terrible moosics :P
As for the layer thing, the two songs that are like that, take 7-1, 7-2 for instance. They would be used for world 7, level one, world 7 level two. I got the idea of layering extra instruments together from Sonic the Hedgehog 3. Where Act one's song would be partially remixed and improved upon. I went for the same thing with my music. It's a very lazy way to make many songs for a game with a lot of levels. In fact, I told Rift to do this same method with Project Awakening. Since there are going to be an enormous amount of locations and places that each need a song.