I think you want SDL-Mixer. The docs from activestate are the best for this module. SDL-Mixer . It allows you to simultaneously play different wavs on different channels simultaneously, and adjust each channels volume. I havn't tried to do the mixing without actually playing, but it should be possible. In other words, output to a file, rather than the dsp.

I toyed around with it and here are a few scripts to look at: SDL sound sampler-mixer and Tk Game Sound demo

As a last resort, you could play them through the SDL-mixer, adjuting each channel, volume to your liking, then record it directly off of the /dev/dep with arecord and pipe it to lame for mp3 encoding.

I'm sure it can all be done, it will just take some hacking.