By the way, your issue with sibilance on vocals most likely comes from FET mics versus tube. You can YouTube people demonstrating mics if you are curious. (Check out the Chandler Redd, a very smooth sounding new tube design and see if those examples still bug you).
I am super sensitive to highs on both my systems and real life, and my spontaneous irritation with them varies based on stress, sleep and diet usually. If I maintain those, I don’t have an issue. When those things fall apart, the world becomes sonically horrid, like needles.
Most likely your issue is neuro, and something like neurofeedback can address it. My $0.02.