People like you are doing valuable work. Your cables being great quality will prevent some customers from buying ultra-cheap or improperly made cables. In some cases, friends of mine have damaged the inputs and outputs on their audio electronics because of careless mistakes made by manufacturers.
You are right. And make a lot of sense! First hand experience is paramount. I know that the input impedance and output impedance of certain inputs and outputs - on power amps and preamps for example, or even on integrated amplifiers can be more sensitive to wire, which can change the sound. However, this is rare and not a common cause for concern if you're getting clear, high quality sound output.
On vintage amplifiers including integrated amplifiers and preamplifiers, using the "aux" out instead of CD yielded a clear, sharper, more defined overall sound. Why? because when we look at the block diagram we see that the signal effectively didn't go through much processing at all. It's the shortest signal path.
Likewise, for all new/modern stereo equipment, would-be customers should ask and audition them that way. Sometimes, there is a specific input that has a cleaner signal path; and some sneaky audio dealers perform those cable swaps without the listener knowing in demo rooms; hence why the sound is different.
My original argument touched on how cables SHOULDN'T make a meaningful difference - in other words, in well designed equipment and when properly dialed in, you shouldn't have to depend on the last few feet of wire for audio nirvana. Your power amplifier, preamplifier, DAC, etc. the ELECTRONICS are already doing the heavy lifting!
