Progress made! Since it seemed like it was a version-issue, I have tried to install other older versions. Your information that older version were still available by simple changing the url was very helpful with this. These were the results:
3.5.1: QHY worked
3.5.4: QHY worked
3.5.5: QHY crashed
3.5.7b: QHY crashed

Both cases that had the crashes were showing the identical messages of a version issue with libusb-1.0.0.dylib in the device manager.
So the good news, we're closing in on the issue and I now have a fully working KStars, albeit it being 3.5.4.
Would this give you some clues of what could go wrong with 3.5.5/3.5.7b, either in general, or the DMG image? And most importantly: how to correct it?