being few decades experienced analog circuit designer / sound engineer / and audiophile, I can add:
1) no design whatsoever is possible without obeying standards, user expectations, and measurements! most discrepancy btw measurements and advanced user are related to not sufficient measurements coverage, e.g. phase, low power transient response accuracy, dynamics, etc. measurements are needed for volume manufacturing process, which helps to ensure all units meet design target spec, all components vendors meet their spec, readability, etc! manufacturing quality tests (measurements) include accelerated aging test, component selection, stress test, shock and vibe, etc.
2) listening, by experienced users, is needed to ensure design engineers included in design target spec all what is affecting SQ. unfortunately currently used audio gear specifications are under-specified, which is causing test-actual sound discrepancy.,