Engine: Windows MME effective volume is much lower compared to OPL3
Download the following midi file, put it in your eduke32 folder and launch the game: grabbag.mid
Now set your music volume to 50% and switch between Windows MME and OPL3. You will notice that Windows MME is much quieter than OPL3 at this volume setting, and I would even argue that OPL3 is too loud by default for most midi files.
Now, I know that the post-synthesis volume amplification can be controlled by the console command
mus_al_postamp, and lowering this from 3 to 2 makes it comparable to the Windows MME volume at least on my end. I would argue that the default postamp level should be set to 2 to better match WindowsMME.