Need some treble

Agree with @hifiman5 -- the Lokius gives you a bit more flexibility in the upper range. The Loki Mini does 2K and 8K in the treble while the Lokius does 2K, 6K and 16K. Keep in mind that the highest note on a piano is 4,186 Hz. Everything above that is harmonics. Only percussion instruments like snares and cymbals have any fundamental output over that. 

Seems to me that, if you're not hearing high frequencies, boosting them via tone controls may do nothing.

Much like having a null in your listening room. 

My question would be. Do those cymbals reappear when you crank it up a few notches?

Go to Costco (etc) get hearing aids

My high frequencies are attenuated, not non-existent, so boosting them makes sense to me.  Getting ready to order my Lokius.

Sounds like the equalizer is your best bet. It is hard to imagine that putting hearing aides in the loop would result in better sound across the spectrum. 
 

Tell us how this works out for you.