What is audible is the effects of phase on signals that are transmitted via separate paths, which is typically the case when listening via stero speakers.Quite so for absolutes. But where there are phase shifts in some frequency ranges, I think they'd be audible.
But the concept of hearing a difference of phase between signals of different frequencis is unfounded.
By definition, a DC-coupled amplifier passes 0 Hz.I don't follow ... a DC-coupled amplifier doesn't necessarily have a frequency response from 0Hz to whatever