I second this request heartily. Just listen to this GORGEOUS main theme!! One of the most stunning tracks I've heard all year in any medium.
https://www.youtube.com/watch?v=hi4aNBc4Z3k&list=RDhi4aNBc4Z3k#t=29
Not sure how many other places it's available but the score by itself is definitely available on Steam (
http://store.steampowered.com/app/475210/). I don't believe it actually requires the main game as stated, it just says that because its filed as DLC and DLC is supposed to need the main game to be playable. Which is not relevant for soundtracks.
The entire score is available on Youtube, we could extract it at 128kbps but I'm too quality-sensitive to really enjoy that. I may buy it myself eventually...