Dear @mijostyn : You are biased on that frequency range were our ears are more sensitive and you said that Wilson on purpose did it " something " in its crossover as other speaker manufacturers and some recordings labels some times but all those just or did not happens in the past or does not happens today. No evidence at all.
After all the information that I read over my research about I don’t need your notch filter. My system handled really good sibilance, not that does not exist but it’s not a true problem.
In today re-issues as the Rickie Lee Jones " It’s like this " you can be aware how the recording engeneer/producer of that Sheridan LP was made it: putting up-front her voice and due the tone of her voice the recording makes a little or to much hot down there. In the first track when you listen the word " shake/shaking " I noted a little sibilance but a very high volume.
Anyway, you can follow with your biased subject, not me because exist hundreds of speakers with a different frequency signature " window ", thousands and thousands of LP/CD recorded in several different ways and with different frequency " window " and each one of us has too ears with different frequency " windows ". That’s all, each one of us try to fix each one of us " problems " in our room/systems. You pointed out several times how you try to fix it: manipulating the system frequency response.
An audio system is a chain of several links and each one has its own every kind of distortion levels that at the end is the system noise floor level and I think you could have a problem down there because your system sibilance " problem " and how you fix it when appears. Higher system noise floor makes sibilance more apparent, yes that noise at the end means distortion levels.
Through the years and with out really looking to improve my system noise floor level I did it when I change my tonearms internal wire cooper by silver wires, when I changed system cables for Analysis Plus silver/cooper, when I take out all the input fuses in the electronics, when I change the power electrical cable for silver cable, when I changed the fancy/boutique speaker crossover capacitors for Wima/Kemet ones, etc, etc.
The noise floor level in my room/system is extremely low and this helps a lot against sibilance goes down too.
R.