What do you mean 'in disguise'? Could you please upload some of those MIDI sample files? And how do you play the extracted (?) FSB files? (I can't play them - they seem obfuscated somehow)
Yes, they could, but they're obfuscated, and a "key" is needed here. Some bytes at start, they all have in common, so it hints to either a XOR key, or a new MIDI-like format altogether. The sound samples (the .WAV file) are not obfuscated, but they are arranged in some "LIST" containers that suggest a custom reading process from the above "MIDI"s. If there is a xor-key somewhere, it should be (assuming "plain") in one of the game files.