I was not satisfied with my previous settings and tried to improve them based on the sound I was hearing from the KH80. I think my new settings sound quite a bit more neutral, although I was not able to make the bass even flatter due to lack of further adjustments.
Nevertheless a speaker with advanced sound controls including a high pass filter allows for way deeper sound adjustments than simple bass/treble controls.
Here again the smoothened measurement with default settings and my new setting:
