The DAC in my year, 1985, generic, CD player, still resolves CDs with the utmost clarity. Other than some (that I don't rely on recording quality much, anyway) streaming, I listen to vinyl. Heck, I'm still captivated by the difference in just those two (vinyl-CD) formats alone, and also as the most audible, sound quality improvement in my lifetime. Even the earliest DACs were/are more capable than the recordings they play back from.
If there is anything the external DACs are adding, it would have to be it's own, over-filtered color to the sound. What makes them questionable is, out of one side of audiophilia's mouth, the idea of excess filtering anywhere, is undesirable. Speaker crossover networks with the least amount of components in the signal path as possible, and minimal, to no (bypass mode?) tone control circuits in amplifiers allowed, either. At least with the latter, you can control the tone, but if it's just built onto the chips, you are pretty much stuck with it.
I am further put off by the idea of the external DAC, due to the fact that many (not all) of the same people pushing or, swearing by them, are the same ones who can hear cables, and other gobbledygook, and that need 100-1000 hrs of "burn-in" on all of their electronics.
The idea of needing an external DAC come 2021, is proof that this industry has finally eaten itself out of house and home with redundancy. It's also obvious that the next real technological advancement will have to come from some type of recording quality standardization (NOT compression) on the recorded material end itself. To my ears, that's the only difference left between audible perfection, or not. The best recordings, played back on a measurably neutral system, need no improvement.
