If you recorded at a higher volume level that would help the sound quality tremendously. Listening with cheap computer speakers, I thought Scy's mp3 sounded great. If there's any way to turn up the volume on the Mac, that might help.
Was listening through your recordings just now...is that really all there is of the briefing music? The file you recorded comes in at a length of 1:18, which is notably shorter than the original version of that same song in Descent, typically coming in at about 2:55. Considering all the other songs seem to be at the same lengths as their original counterparts, I just want to make sure that really is all there is to the briefing music.
I know of a past attempt to try, but said person was unable to locate the files--they were not stored in the same manner as they would for other versions of Descent, and thus weren't quite sure where they are or what file types they would be in, and if it'd even be possible to extract them and read them properly...but that was the attempt of one person. It might be possible for another to try and have more success, but I leave that to whomever wants to try. As for me, that is a field I wouldn't know enough to be of much help with.