There is a community dedicated to composing on OPL soundcards and we were wondering about your Doom and in general DOS music compositions. First, what program you composed with and are the FM patches available. I imagine they were GM patch banks defaulted by the midi composition, but some folks were asking.In the early days of the OPL soundcards, the "gold standard" sequencing software was Sequencer Plus Gold ("SPG") by Voyetra. The reason for this was it had an OPL instrument/instrument bank editor. It is still available as an "as is" download. It will run in DOSBOX though getting it to interface to MIDI devices is something I've never had time to work on. I've used it to save a few native SPG files as General MIDI files.
Here's a post I put up back in 2013 that should help you some: Voyetra Sequencer Plus Visited Again
To rough out compositions, I used Cakewalk ("CW"). I had been using it for several years already and had it all set up to use the analog boxes for sound output. Having "real" sounds from those boxes helped me visualize (audiolize?) what I wanted musically. I would save the CW files in *.mid format and load them into SPG to create the OPL instrument for each track. I built different instrument banks for the different genres of music.
As I said in the post linked above, I have no idea what I did with the CW and SPG native and *.mid files I created. I also have no idea about the instrument bank files. They may be on some old magneto optical disks, ZIP disks or floppies, and "one of these days" I may get the time to go through those.
This information may help, too. It looks like it could possibly be used to recreate the instrument files by reading the data flow to the virtual OPL FM synth in DOSBOX: Blog post on DOSBOX-VST
I haven't had time to check any of this out myself.
The early 1990's files I created were not GM files and did not use GM patches. The *.mid files that were generated later was me taking the original non-GM files and choosing GM instruments to replace the OPL instruments. Sometimes it was a bit shocking to me how close the instruments I had created for OPL play sounded like the similar GM patches. While the GM 1.0 standard came out in 1991, it really had no used for me in the video game music until years later.
If there are any specific questions that you may have, feel free to comment on this post and I'll try to answer them.