I use a 10 band equalizer. Frequencies are those above 2k (parts of 2k are also included). I tried setting the 4k, 8k, 16k bands to 0.0 db (in the center of the equalizer) and it seems to work but the sound changes, is more flat, less open. I'll explain. I'm using a v-shaped equalizer setting, with the values of 4k,8k,16k set at +13db. If I go down to 0db i have to scale all the other frequencies to have the same equalizer with the same sound but without the treble problem(that's my guess). And that would be possible if Poweramp would allow me to go beyond the +-15db of the equalizer like for example the Realtek driver in windows where you can set it to +- 25db. With a max of +- 15db i can't scale and reproduce the same EQ with the same V shape. If it were possible i think i could fix it but i can't be sure. This are my equalizer settings.
Band: 31: +8.0db, 62: +4.0db, 125: -5.0db, 250: -11db, 500: -5.0db, 1k: +5.0db, 2k: +10.0db, 4k:+13.0db, 8k: +13.0db, 16k: +13.0db
If i were to correct it by setting 4k,8k,16k to 0 as a reference i would get: 31:-5db/62-9db/125-18db/250-24db/500-18db/1k:-8db/2k:-3db/4k:0db/8k:0db/16k:0db
As you can see the bands 125-250-500 I can't set them to give the "V" shape, precisely because Poweramp is limited to +-15db.