It would appear that in DOSBox SVN Daum if I launch the game and then manually change the MIDI device to MT32, it works, but if I attempt to set the MIDI device to MT32 at the .conf level, it will show that I have MT32 selected as the device but actually output Sound Blaster sound.

I've already configured the in-game settings to use MT32. Not sure what I'm doing wrong. Anyone have any idea?

In what game(s)? It sounds very odd that if you have set the game (not only DOSBox!) to use MT-32 music, the game would still produce Sound Blaster music. Maybe if the game doesn't let you save the game config file due to file permission restrictions (read-only) or something, so the ingame configuration is still pointing to Sound Blaster even though you thought you changed the setting?

Also I don't understand what you mean by using SVN Daum? Have you specifically replaced the DOSBox in each and every GOG game individually, with the SVN Daum DOSBox? Remember that each GOG game comes with its own DOSBox, you'd have to replace them all one by one.

EDIT: Also, what OS are you using?

A silly question, but do you have some flavour of MT-32 synthesiser, either the real deal or MUNT? DOSBox doesn't support MT-32 out of the...well...box.

You need to do three things for MT-32 sound to work:

1. You need to have the MT-32 device available in Windows as a MIDI device (not immediately apparent in Windows 8 or 10).
2. You need to have the game configured for MT-32 audio in the game's settings program (SETSOUND etc.)
3. You need to have midiconfig in your DOSBox config correctly set. This will usually be "midiconfig=1" but not if you somehow have more than one MIDI device other than the Windows MIDI synth.

This is really dependent on the game, in some cases you have to launch the setup via dosbox and actually change to MT32 otherwise it'll use the default sound blaster, in some others like wing commander just edit a sound file.

Once it's done you must make sure dosbox recognize your device as well by typing "mixer /listmidi", then use correct device number in the config file.

Alright, so, here is what I've done so far.

1. I replaced the built-in DOSBox with DOSBox SVN Daum which supports MT-32 (for legal reasons, the vanilla DOSBox that GOG sells can't).

2. I've edited the .conf files to set the MIDI Device to MT-32 like so: http://i.imgur.com/Q7DrI0h.png

3. I'm only doing this on one game so far, which is Dark Sun: Shattered Lands

4. I'm using Windows 10. After making that screenshot above, I set the midiconfig=1 and all that did was disable the music as far as I can tell.

But anyway, I do run the "Launch Settings" properties and it asks me to use a separate sound card for music and sounds, so I choose that and I set MT-32 for music, and Sound Blaster 3 for SFX, it says it successfully detects both sound cards, saves, and then exits.

Once again, this is for Dark Sun: Shattered Lands.

So you don't have MUNT or a real MT-32. Both of these work with vanilla DOSBox by the way. I tested Dark Sun: SL with vanilla DOSBox and MUNT, and as you can see, it's working fine (although I'll be buggered if I know what a "Soundblaster Pro 3" is).

You mentioned that you're using the Daum SVN build. Have you added the MT-32 ROM files (MT32_Control.ROM, MT32_PCM.ROM) to your DOSBox directory? These are still needed for Taewoong's build.

What are those "legal reasons"? If you mean you need to have either MT-32 or CM-32L PCM and control ROMs, I think you need them also with the SVN Daum DOSBox as well. SVN Daum may include a Roland emulator (Munt), but it most probably doesn't include the Roland ROMs that the emulator needs as well.

What I propose you to do is:

1. Forget about SVN Daum.
2. Download Roland CM-32L (or MT-32; I personally prefer the CM-32L ROMs) control and PCM ROMs from somewhere.
3. Install Munt, and tell it where those Roland ROMs are.
4. Set the game music sound card point to Roland MT-32/LAPC-1 (by using the game's setup program).
5. Do what jamyskis mentioned above, set the DOSBox midi device to the Roland (Munt) one.

The most important thing is that you are apparently missing the Roland ROMs. You need them either way, if you want genuine Roland MT-32 sounds and not some half-assed approximation (using a General MIDI devide or something).