I tried my Diamond DB on an SB Pro clone called the "Super Sound Origins" by SIC Resource. It uses the Opti 924 chipset and has a real OPL3. This is one of many different clones labeled Diamond MF-009. I profiled the card here: Re: Bought these (retro) hardware today
The GM from the Diamond DB works without stuttering on Duke 3D using the SB Pro setting. So I think that Sound Blaster 16 compatibility may be part of the problem.
I'm going to test with my SS7 box to see if the BX chipset isn't part of the problem too.
UPDATE: I have a CT3900 with a Diamond DB in my SS7 box, so I just tested with that. This is a K6-3+ at 550MHz.
First, I have sound set to "Sound Blaster" and not "AWE32."
When I use 8 voices at 44KHz, there is the same kind of stuttering that I saw from my BX box.
However, when I use 4 voices at 22KHz, the stuttering largely goes away--just a brief hiccup now and then. This didn't happen with the CT2760. Both have DSP 4.13.