Sorry if I'm about to get subjective, I'll attempt to be rational about it.
I notice the mantra 'round these parts that differences between DACs should be inaudible. And, at the same time, considering the older and cheaper gear I [let's face it---WE] have been using, at some point there would be an audio rubicon that's been crossed. I'd say that for most people, that happened when 24/192 became a de-facto standard both for production and consumption. What's that, 10 years ago? So when someone says that DACs ought to sound the same, they are pointing to gear being made right now. But going from a starting point of "now" and discussing the sound of digital devices and headphone amps as being a non-factor takes it a notch too far. There are electronic devices being manufactured and bought right now that Amirm would describe as "broken", that is to say, badly performing gear from an objective, measured POV, sold at all price points. You might own one of them. I know I do.
My recent experience starts with getting a cheap [very] computer. It has terrible speakers. The headphone jack has [thankfully] more than enough juice but the brightness of the sound suggests high distortion. I've been listening to most of my music lately on a tiny DAP, the Fiio M3K. Nice interface, great form factor, whimpy headphone amp. I got the Topping L30 headphone amp. I have both the Schiit Magni 3 and one of Fiio's portable headphone amps. The Magni 3 and the Fiio amp were made within the last 3 years, both are known quantities, measured well for the standards of their day. If I say the Topping is audibly better than those two amps, is it the newness of the product or the possibility that it's that much better when "All headphone amps sound alike, all DACs sound alike"? My guess is that the Topping is that much better.
This was reinforced when I got the Topping E30, plugged it into my computer [they shook hands and that was that] and started playing files from Amazon Music and YouTube. One thing was clear, it was easier to pick out low-bit rate MP3s. And it was obvious that recent remasterings can sound considerably better than my memory, although it should be noted that a lot of classical music recorded from the mid-fifties through the mid-eighties have better remasters now than they did twenty/thirty years ago and a lot of the original vinyl was objectively horrible. All of it really, if you're sensitive to the sound of inner groove distortion. The climax is at the end of the side, can't do a thing about that.
In any case, while differences between DACs 'n' Amps should be inaudible, they aren't. My cheap DAP, my old Blu-Ray player, they were top performers once, but they really aren't anymore. What these cheap and cheerful gizmos do is better than Blingy and Costly gear from 30 years ago, and there's degrees of difference right up to the present.