Back at you. I presumed your experience based on your apparent lack of knowledge about what things make practical differences in audio.
Just for example :
Cables affect jitter in many ways including their bandwidth, their characteristic impedance (length, etc.) that affect the timing and shape of the signals… Ignoring the DAC part of the equation, the jitter and noise interact anywhere in a digital circuit even if you only care about the levels when they are clean. There’s no issue with getting the correct bits, but the timing is another thing.
The edges of the incoming data are almost always used to control a PLL or FLL and you skipped right over the fact that PLLs and FLL’s are only a low pass jitter filter. The clock that you generate for the PLL (or something derived from it) is almost always the same clock that the DAC proper uses and at that point the jitter that came very directly from the incoming edges directly affects the resultant audio. (and there are many measurable secondary effects caused by the noise/jitter all over the DACs’s hardware, power supplies, etc. (We can discus how ASRC doesn’t really fix things either.)
Whether a cable is balanced or not (along with the topologies of the transmitter and receiver) definitely does affect the amount of noise injected in it (or the transmitter or receiver) by a ground loop. The style and quality of the construction, shielding, etc. affects how much common noise cancelation there is in a balanced cable. The quality of the grounds and shielding of the cable affect how much the ground loop current affects the data (or analog) signal by conducting more or less of the groundloop current between component’s grounds vs. the remaining groundloop current in the data/signal lines.
The thing to bear in mind is that many of us clearly hear things down 78, 84, 90dB from FS. (There are many studies about whether 16 bits is enough compared to more, but no one really thinks 13, 14, or 15 bits is.) The ear has the most dynamic range of our senses and is very sensitive (in the right circumstances) to small effects on the order of the things I’m talking about.