@Zach - inside your 'data' folder, you can find a series of .ogg files used in the Perrenial game, as well as sound effects, etc. You could listen to these files using a program such as Audacity. Also, you could replace the music in the folder or add your own. If you want to play your own music in the game, just modify the .map files of the map you want to play the music, and replace the first line with 'MUSIC [your music in the same directory].ogg'
Funny. All your .tmx files are written in an XML format. Coordinates for the tiles, I presume? Well, It's fairly easy to mod, which is a good thing. Maybe I could add my own custom level sometime in the future when the Completed Version comes out.
Also, very small glitch (I don't know if it's intended). The sand blocks found on the beach, which can be moved with the shovel, would occasionally not disappear when I used the shovel. Also, using the shovel on some parts of the sand can cause the player to phase into the blocks. I don't know if this was meant, or anything else. Just observing.