There is a single core optimization option you can check off, which might help with the performance, at least.
Did you try saving and reloading, possibly exiting and restarting the game in between?
A couple people reported a similar sound problem in the topic
No Sound/Music.
You can try emailing support@larian.com, with a description of the problem and maybe a link to this topic (DKS
support page). Unfortunately, though, they are on vacation until the end of the month.
