The GK2 soundtrack, in a partial form, was available as a bonus CD in the "GK Mysteries" release of the game (with GK1 and a novel)... it was, as I said, partial and strangely edited - and the order and track selection were bizarre to say the least...
The full version can be extracted (in lower quality, unfortunately) from the data files on the game CDs. I did that recently, and I'll be converting, cleaning, joining the files, making the cover

, and so on, in a while. I may post more information (and covers

for those interested when I'm done; so far, I have only extracted the files and haven't even sorted them yet.
Similarly, I've extracted and I'm making the full GK3 soundtrack. I already ripped, sorted and converted the files, but I have to join some and make the cover

. There are 153 files I have to deal with in total, and (converted to CD quality) they take up 1200 MB... 151 of those files can be extracted from the game, using its console or a tool like GAPlayer. Two more files, "Beta Theme" and trailer music are only available on the Sierra FTP, though (or maybe aren't available anymore?). I posted a list of those files in another thread (It's better to extract them with the console, because you don't lose the filenames then), and, again, I may post more information when I'm done with it, if it's of any interest. Basically, for the vast majority of the music, you only need the game itself, as they're extractable from within. As for the rest, to make it complete, you need the two extra tracks from Sierra, and the RAD video player + VirtualDub to extract music from the clips (including the end credits).