I figured in the interest of possibly speeding everyone's work on the MIDIs, I'm going to upload a tool I've written that can playback the .dro files you get from DOSBox's OPL capture feature (Ctrl+Alt+F7).
I could upload my conversion program, but for various technical reasons I don't think it's a good idea (mainly, it's currently written to be used in such a way that you re-compile the program for each conversion; in short, not easy to use for the average user). But if you insist you can e-mail me for the conversion program as well.
Anyway, if you download
http://www.geocities.com/guestlevels/lemmings/testdro.zipInside the zip file is testdro.exe, a DOS program. You use it by invoking the program in the DOS Prompt along with the name of the .DRO file you want to playback. For example, if the .DRO file is lemmings_000.dro, you'd enter in the DOS prompt
testdro lemmings_000.dro
The program is actually meant to be used in DOSBox. You're not likely to hear any music if you use it in straight DOS, anymore than you'd hear music in Lemmings itself under straight DOS.
The main feature that makes this possibly useful is, you can mute and unmute individual channels as you listen. The Adlib music synthesizer that the Lemmings music are playbacked on has 9 channels numbered 1 thru 9. Using the corresponding keys on your keyboard, you can toggle the mute/unmute status of each channel. In addition, the "P" key lets you pause and unpause the playback at any point (and you can do toggle the mute/unmute during a pause as well). To stop playback, just press any other key and the program will exit.
So instead of having to tease out the notes of a particular instrument within the haystack of the 4-5 instruments that might be playing at the same time at any moment, you can now hone in to just one particular channel at a time, which generally corresponds to one specific instrument. Depending on the music and your ears, that might be of help. You can also try it on music other than the ones from Lemmings, but be warned that this program does not have proper support for the full features of the sound card, so .dro files captured from other games might or might not playback properly.