Treble like bass is a moving target all because our ears change their frequency response with volume. My last processor had dynamic loudness compensation. It changed both bass and treble relative to the volume following Fletcher - Munson curves. It was very spooky. The system sounded the same regardless of volume. Before that I adjusted the volume to the best compromise for that specific recording. Some recordings sounded better at lower levels, others sounded much better turned up. I am sure everyone has had the experience of a recording that sounded somewhat dull until you turned it up then it sounded fine. The problem with the dynamic loudness compensation was that it could not accommodate to any specific recording, only volume. The end result was that I still wound up making adjustments manually. I made life easier by programming a series of target curves matching the F-M curves which I can select manually depending on both the recording and the volume.
Many people advance the treble trying to get more "air." Some of this is audiophile euphonics. Some a response for suppressed treble in the speaker/room combination. The odd thing is I have not noticed older people advancing the treble to make up for their declining hearing. Owning Sound Labs speakers I opted for Atma-Sphere MA2s given their reputation for driving Sound Labs. Nobody has ever mentioned lack of air or depressed treble. Although the midrange and midbass are glorious I found the sound to be somewhat dark. Low and behold even with the brilliance control turned all the way up the treble started to roll off above 12 kHz and by 20 kHz was down 20 dB. This is all because of the very low impedance of the Sound Labs at higher frequencies and the highish output impedance of the MA2s at 1.5 ohms. Sound Labs will go all the way to 20 kHz flat with the right amp. Fortunately for me the DEQX has a 4 way crossover and the Sound Labs has both a low frequency and high frequency transformers which can be biamped. The current plan is to drive the high frequency transformer with a Bricasti M25.