You're right, and Its difficult to judge a person's intention from text alone. Everything stated in my above post is purely the opinions and intuitions of an enjoyer of music. I have no data nor am I about to provide msasurement or data to support my opinions and they are entirely subjective and based on comparisons and impressions only. I purchased all the aforementioned items with my own money, without a hint of favor or expectations beforehand, if that means anything. I do have decades of training as a classical musician if that has any weight, and way too much time listening to audio.
The comparisons - and no I did not do a scientific study - were derived from using Topping D50iii and A50iii as a basis for comparison to each one, then comparing each to other based on my impressions of how they sound relative to those. Since Topping publishes all the gain, Vrms, and other technical information on their website, that was the basis of my numbers. I simply found that the products I called 'credibly sounding like unity gain' sound extremely similar to the 0db Gain 'Medium gain' mode on A50 iii, with D50 iii running at 5V, DACmode with no volume attenuation (theoretically unity gain). I did use both around 60 Ohm and 300 Ohm headphones to try everything. Anybody else is free to do the comparisons of the items above and offer their recommendations of what they believe is high fidelity or not, derived from them.
In my view 'high fidelity' just means 'does this sound right' and is it approximately at 0 Db gain, since adding gain basically alters the original intention of the audio.
I basically zone onto extremely small segments of various tracks and compare which details are audible and how much at a given time, at various settings per device. I think Topping comes out as a good standard since it is very flexible with its various modes and input options.
I do not understand what E1DA team has done with the volume logic on their device, but its safe to say the sound signature is extremely treblous and also quite powerful compared to a typical 0 Db gain signal. This points to using the op-amps at a maximal output level, then somehow attentuating the volume. This is actually how Topping desktop amplifiers work, since the volume knob on them is actually an attenuation knob, with a low impedance headphone (50-60 Ohm) being extremely loud even at 1/5 of the volume on 0 db gain, due to the high total available power bank. It's also rather difficult to hear treble details with a Topping desktop amplifier unless you raise the volume knob to about 1/3, at which point you'll likely go deaf anyway. This behavior of desktop amps might've been what E1DA was emulating to begin with, but he does capture the full amplitude of sound with full volume attentuation being possible at scale, which I commend - as this is impossible on a Topping amp as treble data disappears below a certain threshold.
You've probably encountered the rather unique tweak program provided with E1DA it since you've been testing it, where attempting to press the volume + or - key on windows will swap the volume logic away from the Tweak app back to Windows, and blow you ears off, or vice versa. I don't think that has anything at all to do with noise performance as the op-amps are likely designed to work linearly under any load. Nor do I review the item poorly, performane wise, but I do find it quizzical in the volume handling department.
EDIT: I understand that there is no such thing as 'true unity gain' output, as its a contradiction in terms to have an amplifier that doesn't apply gain. But in terms of sound signature, gain staging that alters the sound signature of the output is for me, undesirable. I think you have high fidelity, digitally speaking, from any of these devices, but what I'm aiming for is accurate sound reproduction. How exactly that can be achieved comes down to the specific op-amp design, and device's architectural employment of them. We know the CS 14314 has built-in amplification, which in theory should simplify things for devices employing them - but as we can see in practice there is quite a bit of variation in the character of sound from devices employing those chips, so the particular amplifiers being used is only part of the story in any case.
