For those who are curious, here are other tracks in SRB2 taken from other games:
*Tunes 29: Spring Valley from NiGHTS into Dreams - or rather one of the many possible arrangements of Spring Valley's music that can be made.
*Tunes 30-32, 1041: Remasters of music from Super Mario Bros.
*Tunes 40, 109: Instrumental versions of the
"Sonic Electronic" track from the Sonic Arcade music CD. (why do we have two SRB2 tracks with this terrible music again?)
*Tunes 94:
Mix of music from Zero Wing (the source of "All your base are belong to us").
*Tunes 110-131: If it wasn't obvious enough already, these are all from various Sonic games, as well as Final Countdown (lol).
*Tunes 1049: Mix of the 2P Competition Results music from Sonic 2.
*Tunes 200: "Disco Zombie" or Boogie Nights of the Living Dead from Earthworm Jim 3D.
*Ultimately SRB2's main theme itself is taken from the mix of
the Sonic and Knuckles theme track from the Virtual Sonic music CD, which the credits theme itself is actually a snip from. So yes, SRB2's main theme is Sonic & Knuckles's theme you could say!
Otherwise as far as I'm aware SRB2's soundtrack is all original. (Then again, I have no idea about the STJR intro's music.)