Just for fun play music really loud and then attenuate 80dB.
Don't know exactly what your own expectations and your environment are.
I listened again to that Mahler track, from DSD source converted to PCM 24/384. Sounds great, but different, on both my D50s or Aune setup.
This is my desk PC and for the D50s, PC sitting at 50cm only of my ears. I first went for fanless Akasa Turing FX. But found my CPU and SSD get so hot. Added and tweaked two slow spinning fans. I hear no sound nor any breath from there.
My streamer plus Aune player is 1m away from my ears. There I killed fan noises, killed also HDD noises (heads where there ticking and crackling).
I do not hear any pop not on speakers nor on headphones.
I did a lot so to kill noise sources around me. Over 6 years, I only got pops out of my Aune setup for short mains dropouts. Did the same for the D50s setup, killing all noise sources. Moved my 4G phone away from the D50s. The only remaining noises (ticks, pops, weirds) come here so from track contents.
I beleive I have so a quiet 60 to 80dB audible range as long I close my windows (the birds, the meowing cat outside)
That explains why you would believe swapping op-amps would change the sound signature.
Fit a poor quality op-amp in a recent DAC, signature will change. Or fit any of such 6dB valve buffer in your setup, signature shall change.
I am not sure swapping recent DACs will change anything. Maybe due to slight differences in the output buffers stages? Due to chipsets? Or maybe due to their internal clocks? But all show very low distortion and noise levels according to reviews here. This is why I wondered now what plots for -60dB in/out would look like.
Is the ESS hump noticeable? I can't know, the D50s doesn't feature that:
https://www.audiosciencereview.com/forum/index.php?threads/ess-thd-‘hump’-investigation.5752/page-5
On the quad FR was simply extended in both extremes. This is not a FR response issue though.
I did it the other way, shortening my FR range.
On the Aune setup, I have a sub my neighbours don't appreciate. "Makes the walls move!" There I have also an extended detailed treble range, sometime tiring me after hours of listenings. That sounds very different compared to my D50s setup (the sub and treble add a lot there).
My Quad for the D50s is a nice Chineese clone of the 76's era model. Some swap op-amps, I made that choice for a different sound signature. Sounds great compared to the limited NX-50, and not like my Aune setup. Last days, I made some tests with frequencies at 17kHz and above, I ended, because I got headache... I could be sensitive to upper trebles the least.
The Aune, now aged, is driving a Yamaha A-S2100 with more extended and sensitive speakers.
The Aune is of the era where people swapped op-amps or DACs to get out a different signature. I bought the Aune because it was much cheaper and cause I couldn't test nor figure out how exactly a Hegel, a Schiit, a Mytek, Gustar, Audio-GD or a TEAC might sound different (recloking, clocking, output stages).
Aune is AK4495S based. I may at some point order a D90se ES9038Pro based, listen, then return it. But I fear I would get EMI noise with it, like I got some with the D50s before earthing and PSU/USB lines cleanups.
I found also that funy paper, pined by Amir: High Resolution Audio: Does It Matter?
https://www.audiosciencereview.com/forum/index.php?threads/high-resolution-audio-does-it-matter.11/
There is nothing magical about 16/44.1 specification of the CD. It is not like extensive listening tests and research were performed to pick these values. They were selected by Sony and Philips in the creation of CD to balance the recording capacity and fidelity. So at some level the one camp is defending an arbitrary set of numbers.