My experience may be apposite to your situation. A few years ago I had my first 'flu jab, but also had a pneumonia one at the same time (aged about 75). Whereas I never had 20-20 hearing, my right ear lost sensitivity immediately upon returning from the surgery; later confirmed by hospital consultants and many private tests as at least 40% down.
I was very concerned at that time for my life-long pleasure of music sessions on my hifi, but somehow, the brain adapted (?) and even today (80+) I still get a kick from my big ESLs/valved kit. More to your point, I found a superb can amp (soooo much better than the Naim Headline I had before) which improved my Senn. 650s no end. I then bought Focal Elears, with a more distinct and transparent presentation and I find myself getting as much pleasure from (moving coil) cans as from my ESLs; different, but equally satisfying. At no time have I been aware of the lower sensitivity in my right ear; strange but I ain't complaining !
I guess my higher frequency hearing doesn't much exist but somehow, this isn't a music appreciation issue as it still seems to be there. Listening to music through further amplification (i.e. h/aids) has always been a no-no for me on principle alone. I've tested £3K aids and NHS ones; there's a heck of a difference, but still haven't got any, despite being referred for them 4 years ago. Can't hear what anybody says on the tennis court, but maybe that's a good thing !!!!
DO investigate quality cans (assuming you can cope with this listening form; not everyone can) and amp; you may be surprised. Don't know Harbeths except by reputation so can't comment on that aspect of frequency loss. Not sure ESLs would be a better solution here, or maybe more up-front, dynamic and higher frequency biased speakers?