Hook the MIDI out from your PC to your MT-32 and the audio out from the MT-32 to audio in of your PC or amp. You will also need to select the right MIDI playback in your Sounds and Audio Devices Properties control panel (MPU-401). For my Audigy it is "SB Audigy MIDI IO". You must also set your game to use its MT-32 driver. For the old Sierra games this can be done with the INSTALL.EXE. I believe that the LucasArts have to be done with a switch added to the command line. It can also be done through ScummVM.

ScummVM is indeed the easier way to do it, but if you're playing the DOS versions, to find out the switches for that particular game just type the executable for the game and add a "?" or "/?" (without the quotes) at the end of it (depends for some games). The green light under "MIDI Message" on the MT-32 should light up during the game signaling when the game is sending a MIDI message to your MT-32 (either custom settings or the instrument notes themselves).

Thanks people. it's working beautifully.

Had to change my sound card to SbLive!5.1 though, seems like my old ensoniq es1370 pci128 has a very lousy mpu401 interface and it distorts the SysEx messages sent to the mt-32 causing everything to sound funky.

I wonder why do these companies say a certain card supports mpu-401 while it actually doesn't...

Might be just bad simulation or something. It techincally "supports" it but as far as compatibility goes, it doesn't do the job.

I guess these cheap sound cards are mainly for casual users, the midi interface is there for a joystick mainly, being that most games don't even use midi anymore, let alone external midi devices like the mt-32.

Yeah, it's too bad, too. Some of the older DOS games have soundtracks that sound better on MIDI modules than some of the newer digital ones. Granted not many, but still. It's cool to have these external beauties 😁.