The plan now is that the music box music will play in your pause screen menu.
Basically in your pause screen you have your stats and items menu. Before you get the music box, there will be a default song that plays for the pause menu.
To keep that from getting repetitive, you will eventually get the music box. With the music box you will be able to set which song plays when you pause the game or set it to randomly select a song from your library. You will be able to collect songs throughout the game to add to your collection for the music box. Part of the fun will be searching for all of the "easter egg" music box discs.
The music box is only intended to be a fun extra feature, and perhaps a way to add some replay value to the game if you wish to go back and search for all of the music box discs. It will not have anything to do with beating the game or progressing through it.
Anyways, this is how we are hoping to have it work.
This idea is still in the works. But I want to get the song list completed as soon as possible!