@Gorgonzola
Many thx for those measurements, I was looking for something like that.
Some years ago I did a similar experiment with ~the same opamps in a DAC output stage:
- NE 5534 (original ones): they did sound very good to me and I could have lived with those "happily ever after". But after hearing the others, I thought the NEs were kind of veiled/boring.
- LME49720: very clear/clean sound ... yes the proverbial "veil was lifted" thing, shoot me! Maybe the cleanest/clearest of them all. Cannot find any explanation for that in the measurement plots.
- SS3602: also very clean/clear, maybe a tad less than LME but somehow with more "weight". A bit more bass energy and the whole soundstage was somehow 'heavier', like it contained more sound (or 'air' if you wish). A sort of relaxed sound, the kind you'd want with jazz/chillout music. No idea how to correlate any of that with the THD measurements. (also not 100% sure if it was the same 3602 model, AFAIR it looked same as the ones on the Spakos website.)
- Burson V5. Did sound pretty close to the Sparkos. A tad less clean/clear, even more "weight" to the soundstage and pretty much the opposite of the 'relaxed' Sparkos sound: the kind of sound you'd want with hard-rock music. That actually seems to correlate quite well with the Sparkos & Burson THD graphs. (at least from what I know about the audible effects of THD.)
My choice/idea was to use the Sparkos for the late night music sessions and the Bursons for party-time. But since swapping was not so easy (and I am lazy) the Bursons just stayed in. I guess my Burson choice correlates quite well with my preference for tube amps (the Bursons THD spectrum looks quite tube-like).
And no, I did not do any DBT/ABX tests, the only realistic way to do that would be to have 2 devices. I did not. And I am lazy
No idea if I can reliably identify NE/Burson/Sparkos in a blind test, the diffs were not exactly night & day. But I am pretty sure that I can identify the LMEs: their 'clarity' also had a sort of metallic/glassy sheen which gave me a slight pressure/discomfort/pain in the ears (and a sort of light headache) after 1h or so. Yes, I tested that multiple times on different days, same strange effect. I expected to see some H5/H7/H9 in the LME plot but there is only one feeble H2 ... seems to contradict all I know about the sound of THD. But then, my test and the THD plots were done in two very different circuits.
And to finish with another beloved cliche: my ẃife/kids/neighbors/dogs/cats did not hear or confirm any of those differences and I have a strong suspicion that they couldn't have cared less.
All that is of course just subjective "stuff" and one guy's anecdote. Take it as you wish.
It's all free though, so you are not allowed to complain (too much)