Well, your honesty is appreciated. The discomfort you experienced is common. The concentration required to parse such small details is not natural for humans to maintain for long periods. The brain does in fact fill in details which is what makes subjective evaluation so difficult. Your mind will emphasize certain sounds on one listen through, and other sounds on another, even if they were perfect mirrors. It is impossible for the human brain to take in all of the sonic details at once, and because our audio memory is so short, the qualities we think we hear are often an emphasis inside of our own heads.
If you are questioning the DAC, blind test that too. You’ll probably find similar results. The power of the mind to interpret and frame our experiences is quite powerful.
Even if you found evidence of quantization errors, the question is whether it is audible or not. I’m sure there’s variation between playbacks in an analogue chain too, probably worse, but the question is whether or not they are audible.
You certainly did not waste anyone’s time, in fact you are now a participant in the methodology of science. It’s been valuable, and I wish more people had the courage to do ABXing. I’ll bet you in the long run your music enjoyment will increase because of this.