There seems to be an update already some weeks ago on Steam, which (among other things) fixes the annoying sound bug.

Here ist the text:

"Update July 28th 2017
Changelog
- added localization for easy/normal mode switching warnings.
- Fixed video playback issues.
- Fixed sound issues, missing music in some levels, some effects playing through left channel only or missing, etc..

Known issues:
- Music is playing low through rear channels in 5.1 and 7.1 setups. "


When it is coming to GOG?

I've been wondering the same thing!

BUMP

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So GOG, what about the update?
It already exists for several weeks on Steam!

Really, it can't be that difficutl to upload this to GOG!

Thanks!