Equalizer for Mac?

Google is your friend

https://www.maketecheasier.com/apply-equalizer-macos/

https://www.schiit.com/products/loki

I just ordered one too boost my tvs bass for movies late at night sort of like a loudness button. Just going to put it between the tv and my integrated (dual purpose room), bet that would work for your high's. I like the 4 bands as well boost/cut  highs, upper mids, lower mids, bass. 

You might consider getting a Room control unit. Most of them have the ability to install target curves so you can EQ any way you want.