High quality equalizers

you could experiment also with devices such as a BBE or an aphex aural exciter, the latter has a midrange control that is good at boosting clarity of inner voices, plus a brilliance control on top and a big bottom" bass expander, as folks with presbycusis tend to lose bandwidth at both ends.  

Just picked one up from a Agoner in Michigan!  Couldn't recommend anything more.  Great for apartment living with limited speaker placement or hearing loss, et cetera

Connect-in before or after preamp ... couldn't discern notable difference; though I like it after so all sources can be adjusted.  Well made!!  You won't be sorry!

Hello,
The Shiit LoKI mini + is the Las test by the company. You can adjust the highest and lowest settings by 6db and the two mids by 12db. At $149 it’s very reasonable. I use this for my phone setup since it is single ended and lets me micro adjust the Schiit Phono stage to get dialed into my system. My preamp has a loop function so I can turn it on and off as I please but it is really for records due to my TT setup is on the light side. Another option is a used older equalizer which has a lot more adjustments and some cool lights. My local shop I frequently shop at in the Chicagoland area has used equipment you can try before you buy. https://holmaudio.com/
It’s like the ultimate candy store. 

If you stream roon has an eq setting you can use.

The Shiit LoKI mini + is the Las test by the company. You can adjust the highest and lowest settings by 6db and the two mids by 12db.

It's actually the other way around. 12db adjustment for the bass and treble and 6db adjustments for the two mid bands.