SpritesMind.Net

Considering some Mega Everdrive goodies for Mega Swirl, in particular a feature that allows you to play background music from audio files stored on SD. Is there any audio compression format the 68k is capable of keeping up with?

Only the most simple forms of ADPCM or CVSD. Actually, the Z80 can handle both of those without the 68000. You need an SH2 (in the 32X) for higher forms of audio compression. See my 32X demos on ogg-vorbis as an example.