The Source Hunter DLC includes a selection of 22 tracks from the soundtrack.
I don't know of a guide for extracting the rest. Did you try something like Dragon UnPACKer? Or check here.

The composer, Kirill Pokrovsky, has most of the soundtracks from the earlier Divinity RPGs (and more) on his website, in mp3 format.


The next large update will make some balancing changes to skills and abilities, and add some new ones (like dual wielding). There should be an announcement about it this week.