I've often wished we could use the ST Original music for hand-to-hand combat. It's just not quite the same if you're brawling with a bunch of Nausicaans or whomever if you don't have the 'Kirk delivers yet another double-handed chop to the back of some alien' music going.
That would be totally awesome. Imagine if you could have the game play the music from the Trek series or movie that you liked the most? Would be nice but Cryptic is far too busy. Maybe two or three years done the line.
AFAIK, there are, indeed, legal limitations on just what assets can be used -- by way of illustration, a licensing agreement can be negotiated to limit the use of characters, places, etc, to one particular movie or series.
Obviously, STO's license is far more extensive than the limited example I've given (and they've already adapted much of the new movie's material), but the licensing of music follows a much more complex path: the recording company has to be contacted for permission, the artist must agree to release the rights to the song, be compensated and paid royalties, and any artists that contributed to the song usually have to be paid their share of the royalties, too.
Not to mention that licensing fees for a piece of popular music are enough to fund STO for months on end....
I have to say the STO music has been the most disappointing music I've heard in an MMO recently (please note, this is my opinion)
Other MMOs have quite epic sounding soundtrack pieces and almost all give a soundtrack as part of their special editions. STO is the first one I've encountered with mediocre music
I was expecting some big orchestral sounding moments in STO for suspense type moments, some strong battle music during combat. So far I have been really disappointed
I've been using the music player and playing my collection of Trek soundtracks, but it is not the same, as tracks do not play at important events. Unless Cryptic could create a hook in system, where I could designate my tracks to be played at certain events inside the game.