Hello colleagues,
So reticently I realized that I can hear up to 15 000hz (I'm 32 years old)
I like rock and metal music and after I bought descent and really flat set of headphones (Sennheiser HD25) I realized that Some high frequencies are really destroying the sound (especially in higher sound register) of the songs. So with really deep research I've manage to achieve really nice sound from my setup - clip zip + rockbox + sennheiser HD25.
I will share my Setup and I really hope that you will also like it. I have change only heights of the sound when I cutoff frequencies around 9500HZ and some minor EQ changes + crossfeed

So I hope you will like my settings

bass: 0
treble: 0
channels: stereo
stereo_width: 100
Crossfeed:: custom
Direct Gain: -1.0 Db
Cross Gain: -12.0 Db
High Frequency Attenuation: -16.0 Db
High Frequency Cutoff: 700Hz
eq enabled: on
eq precut: 0.0 Db
eq PF 1: 200Hz, 0.9Q, -4.0 Db
eq PF 2: 9500Hz, 2.8Q, -6.0 Db
Dithering: off
Timestretch: off
compressor threshold: 0
compressor makeup gain: off
compressor ratio: 4:1
compressor knee: soft knee
compressor release time: 600 ms
With this setting Percussion are really nice and warm. And for me for rock and metal the sound is descent.