I would have a special .ini for the GUS and DOOM in petto, but i didn't used it so far, this .ini will restrict the instruments the GUS can use to exactly those which are needed by DOOM to optimize memory usage, but this dude worked with a real GUS, a 256k release i guess, we can use a whole MB and won't need that. But it could be of interest if you have a large patch set (more as 4MB).

I see that you use "defend" personally i never even peeped into it, a special setup, DOSBox config, is in all cases the better solution as a "one size fits all" solution.
Likewise humans are different shaped, games are different shaped as well.
Apart from that there is no substitute for a special DOS game wrapper which uses images and sounds from the game itself.
Instead that you have to fiddle around with "defend" or similar you just pull the content of the zip to any directory and "press a button" (start a batch), that's what i like even if that costs me many hours to build it.

Recently it will cost me a couple of hours to make that ready because i changed a lot on my default DOSBox installation to run the games and most are "broken" now.
The only drawback (as far as this one) is that my setups depend on some third party software (no fear, all free to use), which is the reason why i have to revisit "DOOM", many programs which i used just a couple of months ago i tossed (that's why i'm not often here, i'm very busy recently but stumbled over your question and thought "i can help you").

As you can see it needs (obviously) a configured DOSBox with a "DOS" directory containing the software i need to build and run the "batch wrappers".
The advantage of this is that you can use my setup for any wrapper i will release, it might be changed but you can always download the latest working one.
And as i said most of all "press one single button" - that's the goal.

It will be DOSBox ECE because of the built in Fluidsynth and MT32, it will contain "Fatboy" as soundfont for Fluidsynth (fatboy is free to share, it will contain most probably an AWE font to just to show off how good or bad it sounded compared to the GUS, 1MB of soundfont can't sound as good as 4 or 8MB that's obvious no? It's in my humble opinion a very meager sound and i can't understand that some are hooked to the AWE, it's brittle and cheap and is to compare to the SB LIVE ROM font which has its charms yes but it's brittle and stiff. The AWE soundfont contains exactly the content of the AWE ROM. Fatboy is phat! it's imho the best you can get, i tried many, about 50 different but i always return to fatboy, "weeds" is fine for its size and also what is named confusingly "fluidsynth" is ok as well. I have to admit that especially for DOOM "weeds" soundfont is very good, just because of the electric guitars and the heavy drums, on the other hand strings will sound better with fatboy and synthetic sounds profit from "fluidsynth". As i said implemented will be "fatboy" but since it resides in a sub-directory "dobox\dos\soundfont" it's no big deal to use any of your like, to make that even easier i will name it to "dosbox.sf2" which will allow you to simply copy another over it so you don't have to change a single word in the batch), of course the GUS is present and working (only what is needed to play games in DOSBox). DOSBox ECE allows me to build these "all in one" bundles where you don't have to care for nothing not even for the meager MSWS MIDI sound.
I recommend not to use a large patch set for the GUS, release 4.11 (which i prefer) or "propatch lite". The guitars (which are important for DOOM) sound quite well and the only bad instrument i found so far is the muted trumpet, it sounds rather like a harp as a muted trumpet. Take care some patch releases i downloaded was "broken" they contained samples which are maybe broken due to repacking or whatever, however that's tard if an instrument has a broken sample it will crackle loud.
This can happen under some circumstances with wave files or maybe even with .RAW wave images (.SND for GUS). I.e. 7-zip isn't safe for such, use only .ZIP for waves else they can be corrupted when extracted, rarely but it can happen and 1 of 1000 is already enough to say no. 7-zip packs all in one long data stream i guess that's the reason for the issue.
It gains a bit compression due to this but it can lose bits, in case for a wave image they can't be reconstructed 1:1 sometimes. At least this is my experience with 7zip and waves and also 7zip themselves state that problems can appear and that 7zip isn't 100% safe it can fail under certain conditions. a possibility is a tarball or just zip it with no compression and compress the zip with 7zip this is safe since file and directory structure is kept by zip no matter what 7zip does to the single zip file.

FYI, the GUS is a bit "silent", means compared to MSWS it's only about 50% of loudness (while MSWS is far to loud and steady above 0dB), the digital sound is even less loud (it seems anyone liked to respect that the GUS is to loud and now it's half of the others - or less). Compared to SB 2.8 times; SB 100% equals to GUS 280% for digital playback, for MIDI it's about 140% as i evaluated to get a peak level of 0dB even for the loudest track i have on my HD, often it ranges about 200% to 300%). This means the SFX will be a bit silent if you run DOOM on the emulated GUS, but of course even about this you don't have to mind i prepped that too and the GUS digital loudness will equal to the SB loudness and the GUS MIDI will respect the loudest track in DOOM (eh, those 140% as i said).

In short terms, the download will be two seperate zipped folders, one containing DOSBox ECE and all what i need as environment, the other will contain DOOM and the files which belong only to DOOM. The intention is that you extract the content as it is to any directory of your choice as long as you keep the internal directory structure, means "DOSGAMES\DOSBOX\DOS\..." and "DOSGAMES\DOOM\...". I could make it more flexible now (recently i fiddle around with "STRINGS" and similar programs to work with env variables) but i don't see a real need for it.
It isn't the last word spoken, since quite a while i'm fixed on Commander Keen and this has priority, i have planned a different DOOM wrapper, similar to what i made for Keen, mouse support and whatever nice things but i didn't even started this yet for DOOM so it will be what i used, what you can see in my many clips i made from this wrapper.
In future music player and game will start with a single batch - recently it still uses two, one to play the game and one to play the music of doom.

The GUS can be problematic - but there should be no issue for GUS and DOOM, ULTRAMID works very well, better as all later releases.
As an option you can run DOOM with MegaEM, but it isn't to recommend, MegaEm uses only 22kHz 8bit downsampled patches, you can't configure it to use something better.
ULTRAMID uses by default 22kHz 8bit patches but can be told to use 16bit quality, overall ULTRAMID AIL2 sounds better even better as the latter AIL3 even when natively supported. It's more flexible because it is a TSR which handles the MIDI stream, you can make a specific .ini for each game - which IS the case for DOOM, it is to find in DOOM.WAD, but as i already said you can make your own one and pass this as option to DOOM.EXE itself just like DOOM.EXE would be ULTRAMID it accepts exactly the same options. One difference there is, ULTRAMID loads patches for all instruments which appear in the game, if there is no space left it can't load certain patches (the reason for the special .ini), unlike MegaEm, MegaEm will load the patches for each track in the game, but the restriction to 8bit over weights this imho.
However 😀 my setup will allow you to try both, native ULTRAMID support or MegaEm. In practical use this means using ULTRAMID it can be that a patch isn't loaded and you will probably wonder when you run the same music with MegaEm where that instrument comes from which was missing before.
I will offer the custom made ULTRAMID .ini together with DOOM but it won't be standard (i guess, i will see... personally i use a "load all patches under any condition" .ini and for DOOM there seems no problem if you have 1MB to store the patches in, DOOM uses mostly the same instruments over and over, it might have been an issue on low specced cards with 256k memory, we have a "crazy" full MB in DOSBox, the 4.11 patchset is about 6MB but that's no problem because of the 196 patches you will need only about 30 for DOOM, i can almost count them at my right hand, guitars, bass, strings (a lot of pizzicato strings - that leaves blisters on your fingers), std drumset, ooh's and aaah's and a often used "guitar fret noise" that's almost all)