Can a digital switch, as the manufacturers and 'reviewers' say it can, improve audio and video streams passing through it. ?
Yes it can. Don't know about video, but audio, yes. The rationale is simple:
It is all about some form of noise (usually either voltage noise or phase noise) hitching a ride along with the digital data (the bits) and getting into the DAC. This causes distortions in the analog signal which somehow affects the human perceptual system. THAT is what an "audiophile switch" attempting to accomplish: getting rid of those noise components before they reach your DAC.
So no switch for me
That was obvious with your first post. So really, not sure why you were posting here. It's not like someone could change your mind and convince you to buy a switch, is it? Besides, why don't you try a switch for yourself? Is it so hard to do?
I am pretty sure you are one of those people from audio "science" forums claiming that all DACs sound the same, and a $50 DAC from China would provide the same SQ as any SOTA DAC. Heck... someone told me there that a DAC is not even part of the audio signal / chain !!