I have tinnitus but I'm not specially bothered with sibilance even so it is present in some songs. I have no experience with de-essers but I don't see why I would limit myself to adjusting only one frequency. Instead I use the Loki max eq. Not often but it comes in handy with poorly sounding recordings. If that does not help, it surely would be your ears and just like tinnitus, the best way to deal with it is to learn to accept it, relax and enjoy whatever sounds you can still hear. Good luck to you.