@Doug - that was it! I switched the mastervolume to 100 in MMPM2.ini and I have sound with SoundBlaster16 Guest and SoundBlaster16 non-PNP.
The sound is still very quiet though. Can you recall what other setting needed tweaking?
UPDATE: it works for new installations. When I tried switching my existing installatation to use SB16 using MINSTALL it did not work.
UPDATE 2: Actually, correction, it works for a clean install using SB16 for both Guest and installer, only AFTER a) changing the MMOS2.INI mastervlume value from 50 to 100, AND AFTER re-installing the SB16 drivers from the SB16 folder on the CD using MINSTALL. I've done this twice now to test and it worked both times.
Thanks to everyone who helped.