An idea just occurred to me. No obligation or expectation, of course: I respect you are busy with these current projects and it is just an idea that may not be workable anyway.
The MK1869 XTREME would seem to be among the most (if not THE most) compatible cards in terms of the range of sound standards they meet...in ISA terms at least. If combinations can be made, there is theoretically room for a PCI equivalent. I imagine something like a hybrid of the Ensoniq AudioPCI and a YMF 724: on the DOS side, FM synthesis via authentic OPL can be collaborated with 16-bit native digital sound in supported games via Ensoniq's drivers (General MIDI can be either Ensoniq ECW or Yamaha XG depending on availability); and on the Windows side, 3D sound via Sensaura.
Technical issues may preempt the feasibility of this concept, but I know I speak for more than just myself in noting how nice it is to be able to free up a slot in a retro PC by combining the unique functions of two cards into one.
System 20: PIII 600, LAPC-I, GUS PnP, S220, Voodoo3, SQ2500, R200, 3.0-Me
System 21: G2030 3.0, X-fi Fatal1ty, GTX 560, XP-Vista
Retro gaming (among other subjects): https://baronsfel001.wixsite.com/my-site