Well, I've never downloaded a Genesis soundtrack, so it is a bit of a waste of space from my point of view, but do you need the space and/or bandwidth for anything else? From a purists point of view, the MP3 versions offer greater accuracy than the GYM's can...does anyone care enough though?
you are missing some DAC sound, but that's it. Gyms are usually Smaller than MP3, and accurate if the GYM player is a good emulator. better than MP3s, as MP3 is a lossy compression scheme, that doesn't save all the original sound.
I know this may be a copyright infringement or whatnot...but how about DC soundtracks (SC5, Samba, Rez) come to mind. I know they're newer and all, but the tracks are hard to find, and they're damn good.
This will sound horribly selfish but NO NO NO NO NO! Keep the mp3s!
GYM files are inferior because 1) no GYM player has 100% accurate emulation of the YM2612 and PSG, and most GYM players use the same emulation core (the one from MAME). 2) GYM files with a lot of PCM (DAC) audio occasionally end up bigger than mp3s if they are recorded for the same length of time. 3) This may be just me being a purist, but the "softer" analog output of the real Genesis (headphone jack) is very preferable to the sharp, hard sound of a GYM player at 44kHz. Also since the PCM audio is typically at a low sample rate in the game (usually 8 or 16kHz) it gets all noisy when upsampled to the 44kHz frequency. 4) This is arguable, but there seem to be tempo problems with some GYM rips, I don't know if this is a weakness of the file format or just the players/emulation.
Either way though, I do suppose that a GYM is still better than a VQF
If it's space concerns, I recommend encoding the mp3's at 96kbps 32kHz... there's no reason to use 44kHz encoding, and you will get significant savings in file size too (should be same size as a 96kbps VQF).
My understanding is that GYM has some inherent limitations that will always cause it to be inaccurate on some soundtracks regardless of the emulation accuracy (in particular ISTR reading that its YM2610 register emulation is only frame-accurate). As I recall, the developers behind the VGM format have laid the groundwork for better Genesis logging support, but last time I checked there was no user-friendly way to rip a Genesis VGM. In any case, would switching SX's archive to GYM provide anything that, say, Zophar's Domain doesn't already provide?