@Soukyuu This is an excerpt from their dev blog back in January after kCBT1:
Q) When I looked at the client, BGMs were included as MP3 files. Can I copy them and give them to my friends?
A) You can give them to your friends as long as you and your friends
don’t use them for commercial purposes. But, some of those BGMs still
need be balanced and go through Mastering process. Also some of them
may not be completely worked at our side. It will be better to use them
when you have the client for CBT2.
http://blog.treeofsavior.com/en/?p=270
I believe the audio files have remained almost unchanged since then. Most likely not a priority right now, but we should expect reworked/mastered audio files closer to the launch of the game.
They also talked about a possible OST release. That would be very nice.