I chose the music in the early days of the mod to be trekish, but more "dark" for the federation being as they were at WAR. It is kind of hard to be bright, cheerful, and bubbly like the root beer Quark so fondly compares to the Federation if you are at freaking WAR, and enemy's beset you on all fronts, and this is before the Borg show up.....
The TMP soundtrack (Mainly the V'ger themes) fit that to a tee. For the other factions i wanted something similar, but recognizable. I was going to use Jerry Goldsmith (the composer for most of the trek movies, and TMP series) themes from other non-trek movies like "The ghost in the darkness" for some of the klingons music. My plan was to use as much music from Jerry Goldsmith as possible that fit with the factions. If that failed then use from the various star trek games like Starfleet Command. If that failed then look elsewhere.
What i did NOT want was the main Star Trek theme (in its several variations) relentlessly playing over, and over, and over again. It's nice, but it can get real old real quick. If you noticed in the early releases of the mod i omitted it altogether. We use as much music from the trek movies, and tv series as possible. If we use "other" music. this was my plan.
The Klingons, On top of their canon themes would have used a lot of tribal music, or warrior themes.
The Romulans. Really didnt have much canon music that made them stand out. So i would have used roman empire, or greek themes.
The Dominion, DS9 music didnt do them any justice. They are the "Space Nazi's". So they would have been themed appropriately
The Borg, Self explanatory. Cybernetic Doom!! I think Fisto did a good job with their themes.
I'm cool with the music in the mod as it is now. I saw some retard on ModDB post that the music was "crap".. Psys reply was perfect. "So music from the Trek movies, and series is "crap"?". I refrained from putting my 2 cents in, because the page would have exploded.
As far as "underrated" music.. Trek VI is kinda underrated. Though its not Jerry Goldsmith it is pretty good, and fits the "deep mystery who dunnit" theme of trek VI.
Trek V IMO its music was great. Despite the movie itself being total shit (though Into Darkness took its place as the worst trek movie).
Do not underestimate some of the music from the TV series too. Especially TNG, because it was all Goldsmith.