... all converters sound different. They may not be drastically different, but they are different.
As long as DA-converters do follow the common standard -
absolute linear frequency response up to 20 kHz, above a sharp brick wall filter
- the differences are really minor and, in true blind A/B comparison with precisely equal levels set, hard to detect.
... All converters create sound degradation and loss in comparison to an analog waveform, ...
Anyway, consumers playing recorded music do not have access to the original analog waveform.
I am running a high end recording studio for decades now,
I have, permanently!
Hearing the difference between the analog input, and what is delivered from my digital recording system all the time is part of my daily job.
I'm doing quasi- permanent A/B all day long.
I can assure you, with professional converters the difference, "the loss" is extremely hard to detect.
Remember, in the studio you have perfectly controlled acoustics and best possible monitoring situation, still!
In a recording situation a dozen and more things matter for creating great sound:
The artist's mood, how the producer works with the artists, microphone selections and placements, the room the recording is done in, analog equipment choice and settings, ..., finally all the decisions that have to be made while mixing and mastering.
I could fill a book with this.
The AD converter is not part of this equation, it simply delivers, period.
Recording is comparable to something like inbetween painting a picture and artistically doing a photograph.
Never will we be able to put the artist into your living room, we don't even want to.
We want to create a piece of art, something special that touches your heart.
Coming back to the RME ADI-2 DAC after this sidemark:
What really matters on your side -
The ADI-2 DAC offers the choice betweeen 6 different so called DA-filters.
The shape of the DA-filter is what affects the sound of a DA converter by far the most.
There is an inseparable, physically link between linearity in the upper octave's frequency response and precision of impulse reproduction.
"Sharp" would represent what is standard for 99.999% of all converters on the market, now you have 5 other options to choose from.
Personally, I use "Slow" quite often.
You can find detailed explanations in the manual page 56 ff.
But I suggest to use your ears to select, graphs may cause pre-justice and can be be misleading.
Finally: While in that, try the "Phase Invert" between "Off" and "Both" (NOT "left" or "right"!). Might be the difference will astonish.