I know, I know. It's basically just parts of the Star Wars soundtrack in midi quality, but there is great charm within and I would very much like to see it added as a bonus.

Actually it's mostly original compositions.

I don't know about the original version, but there's a fan arrangement available; search for "Dark Forces" + "Kenneth L. Simonsen".

Personally, my favorite soundtrack version is the Mac one (which I understand Gog doesn't have the rights to). It'd be nice if some dedicated fan would record and upload it; but I sure don't plan to.

You can also apparently extract the music from the PlayStation version, if you have a copy. (I've personally never heard it.)

I took a shot at the main titles a while ago:
https://soundcloud.com/laserschwert/dark-forces-main-theme

But Kenneth's version of the soundtrack is still fantastic!