Until quite recently I agreed with you. But listening to very loud music exacerbates problems.
I was using the default wiim ultra filter: Linear Phase Fast Roll-off Filter type.
I found the song All By Myself by Celine Dion (1996) was harsh in the treble at very loud volumes.
So I tried all of the wiim ultra filters in the order that I'd prefer next best looking at their frequency curves. Every one sounded better each time.
The last one I tried, the one I least wanted to sound best knowing the frequency curves, was Corrected Minimum Phase Fast Roll-Off Filter.
So I used that filter for all my listening, loud and normal, and actually found I was enjoying all the music more.
This intrigued me so I started reading up on DAC filters, which is when I learnt about NOS. On examining the Fiio K11 R2R frequency curve I saw it performed almost as well as the wiim default filter, only down about 2.5db at 20khz, so I thought to give it a try - I do prefer a DAC respecting a 20hz to 20khz flat frequency response, but it's got to sound good with all music I listen to - I don't like fidgeting with tone controls.
And now I'm enjoying the music more at any level using the Fiio NOS mode DAC.
I must reiterate that I could only decide a difference at very loud volumes. And can fully understand one not being able to hear the difference at normal listening levels.