First off, you need to get yourself a new (hopefully better sounding) MIDI soundfont. (.sf2 files)
If you're feeling crazy and have too much hard drive space, here's a large collection of midi soundfonts on archive.org:
500 MIDI Soundfonts Collection[archive.org]

Alternatively, simply look up midi soundfonts via your favored search engine, and download only a couple. I have yet to find one that sounds "perfect" but they all sound better... even the Nokia soundfonts.

Simply open the game's installation directory (C:\Program Files (x86)\Steam\steamapps\common\STAR WARS Dark Forces Remaster) and replace the 'Roland SC-55.sf2' file in your game directory with the new one, whilst making sure to give it the exact same name. This way you won't have to mess around with the console!

This method is better if you don't plan on messing around with different soundfonts, and the guide already ends here if you choose to go this route!

Once you have found some .sf2 files, simply open the game's installation directory (C:\Program Files (x86)\Steam\steamapps\common\STAR WARS Dark Forces Remaster) and throw the files in there.



Yeah, just chuck 'em right in there, next to the executable.
Next follow the step below.

Now whilst in-game press the tilde key (usually the key underneath ESC, even on non-English keyboards?) and type in the command:
im_soundfont namegoeshere.sf2
Obviously with the file name replaced.



It's important to either remove all spaces from the filename, or to surround your filename in quotes.
For example: im_soundfont "name goes here.sf2"

Next, close the console by pressing the tilde key again, and go into the game's sound options. Switch the Music Type to 'OPL3' and then back to 'General MIDI' and bam, it's using your new soundfont!

Should you follow these steps and you only hear stuttering instead of music, you likely did something wrong. Press the tilde key again, and you should see an error message informing you of what's going on. Usually this happens due to a wrong filename, or leaving spaces in your filename.

When loading very big soundfonts, the music may also stutter and the game freezes for a second or two, as it loads it all into memory. With the biggest soundfont I have (Musica1.7 - 1.84gb !) it took around 6 seconds.

You can also try adding quotes to the soundfont's file name, if all else fails.
For example: im_soundfont "name with spaces.sf2"