Phil did a video on this. If you haven't seen it, it's worth checking out: Roland MIDI Emulator Project 2.0 for best music with DOS Retro Games

softmpu with a null modem cable is the easiest way to handle outputting midi from a dos setup to an external pc. for win9x there are roland and yamaha serial midi drivers you can install; for winxp & up you can use hairless midi serial bridge. in lieu of a direct connection to the windows midi mapper, midiyoke (or midiplayer6 in a pinch) will help get that serial midi data to the softsynth or hardsynth of your choice. i have a win98se setup so i can play mt32/gm streams with the following softsynths:

munt
roland vsc
yamaha s-yxg100
timidity *
qsynth (fluidsynth) *
midiplayer6 (bassmidi & vsti) *#
casio sw-10
websynth d-77
wavecube
wingroove
* soundfont capable
# munt vst, roland vst, s-yxg50 vst playable, but roland scva needs winxp x64 & up)

you can also use midiox in your workflow to remap gm instruments to mt-32 mode so you can hear what these softsynths sound like in mt-32 games that use default instruments like monkey island.

With the right adapter / cable to convert the game port to din midi you could look into the Roland um-one.
I use that method or the serial softmpu method to a mt32-pi. It would for pc as well.

From what I read on the net, I believe Roland USB adapter is a good option. I tried a cheap modern adapter when I wanted to get MIDI ouput from a PC into a laptop running MUNT and it simply failed 🙁

There's this interesting project, but I am yet to try and build something out of it, although I have some PCBs and can even share if people are interested (min batch was 10 boards)...