Sound card is Sound Blaster Awe 32 PnP. It does not or should not need SoftMpu.

Did a quick test with my AWE system, both games, no external midi though.
I don't get the lockup, but if I change the sound card to either roland device, it'll switch to "no card" when I hit return to menu.
and no sound in game, although I do get sound at gremlin splash screens when the game loads.

The fact even though the sound card is set to roland yet the gremlin screen gives sound would suggest it gets its settings from set blaster line maybe?
I'm using A220 I5 D1 H5 P300 E620 T6 for what its worth.

Yes, if I don't connect Roland, it will switch to NO CARD just as you say. But if Roland is connected, it will hang.

But it happens only on my Pentium machines and Sound Blaster. Perhaps time for SoftMPU? I tried it on 386DX and everything works out of the box! 🤣

Just a note: standard midi address is 330. You have 300. I always use 330 for external midi.

Last chance I will try is: Sound Blaster AWE64 + SoftMPU. Otherwise I'm moving to 386DX and perhaps upgrade to 486DLC. Some noname soundcard on 386 that also has connected gameport and cd-rom is working out of the box, haha. That would kill me.

Yeh network cards on 300 and as none of my games are hard coded 330 I'm going with the old rule if it aint broke... as I find dos networking is very easy to go from working to broke 😜

Ah my tests were on a 5x86 so probably not that much use even if I had an external midi device.
I can imagine it been a speed issue, especially as it seems like the game does check for a midi device. Probably worth slowing the Pentium down as well for testing

So communication with midi in this, lets say Amiga PC port, might be caused by fast CPU? Because some even older games work and play MT-32 on this machine, but they are not Amiga ports. And I get this same issue with Chaos Engine CD version, which says on cover: for 386, 486, Pentium.

I tried some slowdown utilities: slowdown in Freedos, moslo deluxe, throttle. They do not work reliably. Few seconds it will slow down and then few seconds it run faster. The instruction flow is not at constant speed and it also breaks midi music. As a music producer I would say the instruction dance on shuffle groove, the timing of the drum beat is off 😀

It's all just guess work on my part. but I can imagine an Amiga port not been the best coded game and maybe midi communication happing faster then the game expects or can handle.

SoftMPU can be used to delay the signal, maybe worth a shot?
"The optional /DELAYSYSEX switch enables small transmission delays to prevent buffer overflow with the Rev.0 MT-32"
from http://bjt42.github.io/softmpu/