I wrote something down here, but it is about workarounds on the driver's side. One being an interrupt tweak, another is increasing the DMA buffer.
Doom 'MBF' for DOS, Maintenance release 2.04

I don't have any SB16-based sound card affected by the hanging note bug but I'm aware that there is a workaround written by NewRisingSun: FixMPU: Software solution for "hanging note bug" on SB16 with DSP >v4.06 <v4.16

On Windows 9x with PnP or pseudo-PnP Sound Blaster cards, it should be enough to change the port in the Device Manager. The Creative drivers will sync these settings with the BLASTER variable and initialize the card accordingly in DOS mode. From there I take a route similar to yours, I use a different card for MPU-401, in one of my builds a Vibra 16S integrated on the motherboard works peacefully with a Turtle Beach Maui.

I'm not 100% sure, but disabling the MPU-401 on a Sound Blaster might also disable the ability to use the AWE32 EMU8000 via MPU-401 in the Windows's DOS box, so personally I just set it to 0x300, since this port can often be configured for the MPU-401 in games. I can check later this month what happens if I disable the MPU-401 on the SB16 part altogether.

If you're adventurous, you might check the SB16 WDM drivers taken from Windows ME to 98. This might also work, since the MPU-401 is routed by the drivers to the device you select in the Multimedia control panel.

Gmlb256 wrote on 2023-07-31, 20:32:

I don't have any SB16-based sound card affected by the hanging note bug but I'm aware that there is a workaround written by NewRisingSun: FixMPU: Software solution for "hanging note bug" on SB16 with DSP >v4.06 <v4.16

Thanks for this! I've been cooking up a music related project myself and I think incorporating that technique into my own player will be really worthwhile.

GL1zdA wrote on 2023-07-31, 20:55:

On Windows 9x with PnP or pseudo-PnP Sound Blaster cards, it should be enough to change the port in the Device Manager. The Creative drivers will sync these settings with the BLASTER variable and initialize the card accordingly in DOS mode. From there I take a route similar to yours, I use a different card for MPU-401, in one of my builds a Vibra 16S integrated on the motherboard works peacefully with a Turtle Beach Maui.

I'm not 100% sure, but disabling the MPU-401 on a Sound Blaster might also disable the ability to use the AWE32 EMU8000 via MPU-401 in the Windows's DOS box, so personally I just set it to 0x300, since this port can often be configured for the MPU-401 in games. I can check later this month what happens if I disable the MPU-401 on the SB16 part altogether.

If you're adventurous, you might check the SB16 WDM drivers taken from Windows ME to 98. This might also work, since the MPU-401 is routed by the drivers to the device you select in the Multimedia control panel.

This is useful information, thanks. I haven't had an AWE32 or 64 for a while now, so I'd really like to know what the effect of this is. I imagine there has to be a good reason they had made the distinction between MPUEN and MFBEN.

MFBEN is for connecting emulation IRQ to NMI of the motherboard so that TSR can emulate MIDI stuff when the card hardware gets any MPU401 accesses.

But as far as the cards go, you can put the MPU to another address. UNISOUND should work with most/all the PnP SB varieties that lack the jumpers, and can do that for you with more convenience than Creative's own drivers.