Just a quick update on my previous comment about 'hardness'.
I hadn't spent time in 'breaking-in' this component.
I let it run over several days, with zero level audio amplification, and found that the 'hardness' was less noticeable.
Maybe still a bit fatiguing.
I have an equalizer, but it operates in the 24/96 digital domain only.
This really needs some EQ on the SU-1 analog output, or on the amplifier input.
I just received a Samsung USB-C dongle/cable with DAC/Headphone Amp - and the improvement in clarity is something that I was not expecting. Never heard anything sounding so clear, and in some cases where the music already includes distorted elements, it's so easy to hear - e.g Amy Winehouse's music.
For now, I had to implement a slight tilt EQ/slope, with some boosting of the lower frequencies, to soften up that high end.
A lot of the music we listen to, has more high frequency content than we would imagine, cos in my opinion either that's part of the genre/production style, or its cos they were produced on speakers with not very transparent high end.
So the advent of much better flat frequency converters, is a double edged sword. It takes a bit of acclimatisation.
But it depends on the music or audio we are listening to. I think today's dacs are simply delivering what was in the audio - and we are the one's surprised.
It would have been interesting, if the OP was genuinely inquisitive, and not a troll, what reference music they were listening to, to arrive at the opinion, that the SMSL SU-1 was "sharp" and fatiguing.
I'm listening now to some Bebe and Cece - their greatest hits album from 2003. Many years ago when all I had was a CD player and I was listening to these on really cheap headphones, I came to the impression that the album was bass light, but having the confidence that my "new" acquisition is NOT lying to me, it's so much more obvious, that this album is bright, but its the music, and NOT the DAC.
I think what a good DAC does, is show you how different every track is, because it adds no colour of its own. Every piece of music/audio becomes a revelation - wow - I did not know that was on the track !.
But then I listen to some Norah Jones(Come away with me album) , and there is nothing "sharp/treble prominent" in these songs, just clear, and so easy to hear every word. No possibility of any fatigue, none.