As you know, Sonic Spinball used the GEMS sound engine, which made it a lot more user friendly to directly program MIDIs into the game. Recently, the game was ported to the mobile phone (including the Windows Mobile OS) from the original source code, since the source code was in C. As a result of both the source code being available and that the game used GEMS, they used the MIDIs for some of the sound effects and music in the game. I'm very very sure these are the original files; the file names are unaltered and gives us a clue as to how many versions there were for some music (from what I see, just two, but who knows).
For instance, if you remember - some of the game's music was replaced in later revisions of the carts for obvious reasons. But since EA was so nice as to supply the MIDI files with their original file names, we can get an idea as to how many versions there were of some songs. For example:
The original title screen music was the Sonic 1/2 theme, but besides that and the one that's used in the final - there were two other versions made. What they could be, not sure.
But anyway, here are the MIDIs. There are a total of 24 MIDIs from some music and a lot of sound effects. It's obviously incomplete - and I checked every single version of Spinball that was ported to the mobile phones and couldn't find anymore.
But whatever, enjoy!
(I wonder if the mobile phone ports of Sonic 1/2 are using any original MIDI arrangements? It's possible that while in the process of programming them in the SMPS engine, they were altered from the original MIDI arrangements. Still, I doubt it - but it's food for thought.)