Hidden within the final game exist two files not used ingame: silver_theme.xma, and shadow_theme.xma. These aren't used, instead theme_shadow.xma and theme_silver.xma are used. So what are these extra theme files for? Turns out, that when the files are swapped and played in the sound test a different song is played. For silver_theme, a version of Silver's theme plays that has no vocals. Instead, what appears to be some sort of MIDI backing is used in its place. This was probably used before the song was completed, and they needed some sort of placeholder. This is further backed up by shadow_theme, which is simply a version of "All Hail Shadow" from Shadow the Hedgehog, unchanged. Additionally, the demo version of the game had a main_theme.xma. Swapping a file such as theme_sonic.xma with it gives a version of "His World", also with some MIDI backing in place. These were most likely used during recording of the vocals to make sure the singer didn't jump ahead to a different point in the song, and to keep a good tempo.|
Download main_theme here.
Download silver_theme here.