Connect the S2 to the Music Quest MPU clone's wavetable header. You want to default its IO to 330 for most games, some older ones might require 300 but most look for 330.

For the SB16, set its MPU401 to 300. If you have a PnP SB16, use Unisound and you can skip the MPU initialization altogether.

After everything is initialized, the SET Blaster statement should have the MPU401 setting as 330. The Music Quest will output wavetable audio, as well as send MIDI to an external module. So switching between them is as simple as choosing the audio out from the Music Quest or the external module.

SScorpio, thanks for the detailed response. I omitted something in my post; I'm trying to avoid using the wavetable header on the Music Quest MPU close, purely to avoid cabling headaches. I have no free inputs on my mixer, and prefer to use the mixer, rather than pipe midi devices back through the SB16. However, if using the the wavetable header on the MPU card is going to avoid creating further config headaches, I could always disconnect something - just I rather enjoy everything cabled up and ready to go, without having to plug cables when I want to use another PC.
Thanks!

The MPU401s on SB16s are mixed bags and most (possibly all) have some issue. It could have the drop notes bug that's easy to verify in Doom 2, or it might have the issue where MIDI has problems when using 16-bit audio.

Since you are using an external mixer, you'll probably have a better experience using the wavetable on the Music Quest. Since that and the SB16 are separate outputs, you can easily control the levels of each right from the mixer. If you were using the SB16 you'd have to rely on a software mixer. Some games mess with volumes when they launch, and not all games have in-game sound volumes.

Good point, and I'd forgotten about the hanging notes issue on the SB16, which mine does suffer from, at least on externally connected modules. I'll stick the daughterboard on the Music Quest, thanks for your advice!

So there's still a part of this I'm not clear on... The MQ MPU clone is already in the PC and functions as a MPU-401 type device, and works with external modules. Currently there is nothing plugged into the audio jack on the MQ MPU, as the device is not creating any sound, that's handled by the external devices. I'm not clear if there is a 'switch' that tells the MQ MPU to use either an onboard wavetable board, or the external midi devices, or if midi data is being sent to 330, both wavetable and external midi are active and it's just a case of muting the mixer on the one you don't want. I think I'm missing something really obvious here....?
Thanks

OK an update, I've got the waveblaster connected to the MQ MPU, and I routed the audio output into the Line In on the SB16 to simplify cabling and it works great. Using Doom and selecting Waveblaster, all audio comes into the mixer from the SB16 (as is should).
My issue now is when I select Sound Canvas, I still get audio from the waveblaster. Is there a way to turn this off? As I want the digitized sound from the SB16, I end up hearing both the external soundcanvas along with the waveblaster...

Hi!
Well the pcmidi audio output is a "dumb" one, there is no mixer or way to cut off sound unless you disconnect the cable or mess with the sb16 mixer app and mute line-in

Thanks! I think the real solution for me is a mixer with > 4 inputs. If anyone has a suggestion I'd love to hear it 😀