All of these tracks are phenomenally great remakes. My only complaint is track 06. The original of that particular track had a soothing effect that your remake just doesn't have. Regardless I think this is one of the best audio remakes I've ever heard, not just in the Marathon universe but gaming in general.
The music that is shipped with the Marathon release is based off of the classic Quicktime synth. This is the fed through fluidsynth which utilized a modern sample set — in this case, Don Allen's Timbres of Heaven. All tracks have been normalized and made working for in-game.
To install, simply replace the Music folder within the Marathon data folder