Sonic 2 MP3 Tool v1.2
What this tool does, quite simply, is synchronise with your Megadrive Emulator to play MP3 tracks instead of the music built into the Sonic 2 ROM. It does this via the magic of memory hacking to access the Emulated Genesis RAM RealTime. It currently supports Gens and Gens+ (no longer Kega Fusion), though please email me if you want another emulator added.
Download the tool here or here (mirror)
I've now created a bat file, which when placed in the folder of the MP3's from the Sonic 2 remix project and ran, renames the files to their appropriate "soundtest number" name. You can download this bat file here.