Yeah, here it is, I believe. (It's an FTP link, so it might not directly download in newer browsers.)
Quoting the relevant part:
QUESTION: Mega-Em gives me a warning saying I have a pre 3.xx UltraSound
board and Roland emulation will not work with […]
Show full quote
QUESTION: Mega-Em gives me a warning saying I have a pre 3.xx UltraSound
board and Roland emulation will not work with most protected mode
software. What gives?
ANSWER: Mega-Em is supporting your UltraSound card as best in can. However
the early revisions of the UltraSound were never meant to emulate
Roland sound devices and do not have the necessary logic to
provide protected mode emulation. Despite this Mega-Em will
still give Roland emulation for real mode software.
Given that TSRs that emulate hardware through (Q)EMM386's port trapping feature don't work with protected mode software, doesn't this imply that 3.xx GUS boards in fact do generate NMIs for MPU-401 emulation? Or is there a another way to perform hardware-assisted emulation?
EDIT: Actually, the question above the one I quoted (about OS/2 not being supported) explicitly mentions the dependence on NMI.
As for MEGAEM "superceding" SBOS, that was never really true. I remember still being dependent on SBOS as the only remaining fallback for protected mode games that didn't have native GUS support and didn't have native GUS patches available for them.
(And even with SBOS, there were a few stubborn protected mode games that would refuse to work with my GUS. I'm looking at you, Pizza Tycoon! 🤬)
I guess my GUS wasn't one of those later 3.xx revisions. Either that, or I was using an outdated version of MEGAEM.
Sorry for veering off-topic too much.
Back to my main question then: could a DOS32GUS utility be developed in the same vein as DOS32AWE, even if just for revision 3.xx GUS boards?