I've noticed this annoyance in other DOS games, not just in EWJ.
For example, for Redneck Rampage, I just plainly disabled the music, because it was way too loud and I couldn't hear my surroundings. There are other games that, fortunately, let you change the volume like Blood, but unfortunately, EJW isn't one of them.
I'm trying to find a solution too. The best thing I can think of is to actually burn a cd with the soundtrack of the game or mount it with a CD/DVD emulator program, like DaemonTools, so that you can control the volume directly from Windows. I haven't tried it myself, but it's the best thing I can think of.
you can use the mixer command to change the cd audio volume.