Nothing is ever good enough, right? But it's possible that that is exactly what might be happening. Many modern amplifiers have such low distortion, cross-talk, and noise figures as to be transparent. You can always argue about the differences between 0.01% and 0.005% THD, but in reality there is no discernible difference.
It's kind of momentous when even the central organ of the audiophile community, Stereophile, admits as much in a review:
Reviewing modern amplifiers is difficult. Unless they are perverse—single-ended triode designs come to mind—all the first-order characteristics, such as frequency-response variations and output-impedance interactions, tend to be indistinguishable from each other.
It's even more notable when this comes in the review of a comparatively affordable (by high-end audio standards) direct-digital integrated amplifier, not a Class-A monoblock that costs tens of thousands of dollars.
This particular amp is also interesting because its manufacturer isn't shy about this being an all-digital, software-defined piece of audio equipment. In a world where analog rules, where tubes are still widespread (and even gaining momentum), where Class D amplifiers are considered sacrilege, that is pretty remarkable.
As their whitepaper says, Music has gone digital. Is your playback system still analogue? It makes sense, and it's clearly where music is heading. And more than that, once software is involved, it can do all sorts of things to improve sound. High-end active speakers are starting to appear that have not only the DAC and amplifier built in for convenience, but have processing built in to match them exactly to the speakers and perform complex corrections for room characteristics, speaker imperfections, etc.
Most of our sources are now digital (with vinyl being the only real exception), why should playback not follow? And with software being able to do everything and anything, we might soon have playback that is, for all intents and purposes, perfect.