Are you saying there are no measurable differences between the component parts (caps, wire, resistors...) that go into audio designs? Or that once integrated into the designs, all DACs, preamps, amps, etc. measure the same? Not following you...
Surely. I am saying that "component" sound per si does not exist in a measurable way. There is no measurement that can explain the differences between the performance of good quality resistors of the same value in audio. The same way for most capacitors. If you replace all the film capacitors of a decent preamplifier with Teflon ones costing 100 times more the measured specification will be the same. If you have good direct evidence of the opposite please refer it.
You will find many different specifications in these components but straight people will tell you that within the audio bandwidth they are not technically relevant. Expensive components in industry pay mostly for long time reliability, stability, reproducibility (consistency) and tolerances, things that do not affect immediate audio performance. But sometimes they must have "magic" properties in sound, because in reality they sound very different.
Actually, you can. There are plenty of amps, preamps, DACs, analog sources, passive crossover networks, etc. that measure relatively high levels of noise and distortion, and compared to the clarity and precision of well-designed active sources playing good digital files, I can hear the difference as well. I'm confident those differences, shown in measurements, could also be easily identified in blind listening tests. Upgraded caps? I wouldn't bet on that being heard, even by trained listeners. Is it possible? Sure. But I'll bet it would have to be an upgrade from one of those really bad caps you referred to above.
Tim
Can you list a few of the bad and well designed components you refer?