Another thing I'd recommend you try are THESE
They're felt rings that you put round your tweeters that help to tone down treble by reducing reflections. They can also help improve the stereo image. I have a pair and found they found they did both. I didn't have a problem with harsh treble at first but it got worse the more revealing my system got. So it sounds like you're in a similar boat.
If they won't fit your speakers then THIS company will make you a custom set.
The Russ Andrews ones are great value for money though, which is something I find can rarely be said about his products.
Source: Apple TV 4K - DAC: Beresford Bushmaster Mk II - Preamp: CI AudioPLC-1 Mk II - Power Amps: Musical Fidelity 550K mono blocks - Speakers: Wharfedale Opus 3 - Cables: Mark Grant etc - Misc: Belkin PF30 mains filters.