I wrote a program which allows you to put custom MIDI files in the Sonic & Knuckles Collection. In this way, one can set up a custom soundtrack. One of the possible applications is to restore the original versions of the songs which have been changed (Ice Cap, Launch Base, Carnival Night, and a few others). But you can also use whatever song you want. The program will be released soon, on the Sonic Retro forums.
Note that this is not a TAS of any mean. In Angel Island I even waste time (and lose rings) on purpose to let the song play for longer.

The MIDI files used in this example are from vgmusic.com; the copyright is ultimately of Sega's sound team, and the arrangements belong to their authors. See vgmusic.com for more details. (less info)