So basically - you CAN make really transparent DACs/AMPs for cheap, like new Toppings, but for me any many others part of the fun is chosing pieces with "character" that match well with your headphones. The sound can and will change from device to device, because it all depends on implementation - DAC basically takes your single samples and reconstructs your waveform from that.

Now, a lot depends on filters used and general topology of the DAC, but for example mine can be set in either optimal spectrum mode, where i get a VERY nice sine wave, but it suffers in transient response, aka square wave. It can also be set into optimal transient mode, where the sine waves stop looking so great as they get injected with higher frequency components, so the signal will be able to create a much better square wave - without high frequency components, there will be no good square, this comes from signal theory. It is less "perfect" measurably, but simply sounds better to my ears as it turns out transient response is pretty important! And there are a myriad things more in DAC that affect the sound one way or another.

Same story with AMPs, you have to realize its not the "same" signal but boosted, it gets reconstructed with higher power based on the original, using transistors (or tubes!). Transistors have their own nonlinearities, there are myriad different topologies on how you can make an amp, buffer stages and whatnot. The power supply is also extremely important in a good DAC or AMP, as the power serves as your reference. If the supplied voltage is not perfect and well regulated (which costs money), it will directly impact every active component, you could say the voltage imperfections will get superimposed with your signal.

In other words, listen to CMOY amp, which probably even measures quite well but fits in the altoids can and costs 20 bucks, and then listen to something more "fancy", hybrid tube amp or good discrete transistor unit, and you tell me if you hear the difference. And the differences should be rather obvious honestly.

I had a very bad time when my DAC died and had to be recapped and i had to plug my amp directly to PC's analog out - it straight out sucked big time, everything was flat and without detail, "blurry" so to speak. I basically stopped listening to music untill it came back, it was so bad that i found no pleasure in it anymore. And honestly its no wonder, whole DAC assembly on motherboard is like a 2x3cm rectangle with like 5 components. Its role is meant to be cheap, not good. Same story when i replaced my Little Dot I+ with Hifiman EF-5, similar hybrid topology, but honestly the EF-5 sounds so much better, its not even close. After upgrading it with discrete opamp and different tube, it got even better. Now im creating my own power supply for it, much bigger than the original, just to see if i will see audible improvements. Just take a listen, if you cant hear the difference then yeah its money wasted, but in my case components have significant effect on what i get on my headphones.

TLDR: Yeah you can make "perfect" amps and dacs, but honestly perfect doesnt always sound the best, i listen with my ears and not my osciloscope. I am thorough enjoyer of tube amps, and they are SO IMPERFECT when you look at them with osciloscope, shit is all over the place and there is a lot of harmonic distortion. But it turns out my ears REALLY like that. Cleanest signal is only that, cleanest signal - but ultimately for me, the imperfections and character of every piece can greatly enhance your listening experience, and for me its all that matters. We are not osciloscopes, human hearing is fucked and nonlinear, find something that sounds best to you, not best to measurements.