I have a similar device, unfortunately it has no short protection (sp?). I already replaced output transistors once on it, cause previous owner shorted the outputs accidentally.
No headphones are picky if you have good gear.
There are exceptions like OTL tube amps and low impedance headphones. But elegia works fine with any new good amplifiers.
And of course has nothing to do with DACs, it's ridiculous.
e.g., realism, 3D, details, tight bass, tonality, attack/power, fullness/thinness, decay - just your feelings. None of that is relevant to audio quality.
Well maybe decay does, but it's not part a dac anyway.
Of course, it's unlikely many people can hear above 20khz. You also need music that has enough energy in that range, and speakers that do well 20khz+.
Combination of all of the above is very very rare, statistically.
That pretty much says that what you hear in D50 and D70 difference: 1)...
They are all absolutely flat and noise floor is at 120db. You are either listening to music in a very quiet environment or you are fooling yourself (and us).
It's also possible you have different filters on those dacs which might affect slightly frequency response past 20khz. Your dog will hear...