Took a break from this and then revisited it briefly today. I used the driver CD hosted on Vogons instead of the driver packages from Phil's Computer Lab, and I didn't run into the same "corrupt package" errors that I was seeing before. No luck with the fixes we've already talked about, though.
One new thing I tried: I found an option to disable the default Aureal wavetable. Now, MPU-401 is the only MIDI option available, but I'm still not getting any sound. Boo.
Also tried going a different route and connecting the waveblaster module with USB, but alas, the XG16S doesn't work with Win9x from the sound of things. Double boo.