Any real difference in RCA cables quality for sub?

If the power cord affects it like that this tells me the Aurender is using batteries to avoid building a more expensive power supply. But if the batteries are connected to AC then all the AC line noise can ride across the batteries same as it rides across even a very expensive power supply. Think about it. If power supplies worked perfectly power cords would not work at all.

Well, it would not be the first time something in high end audio defied my intuition. i remember my first digital interconnect... 1989?... it couldn’t possibly effect the sound, but the largest difference I ever heard. I long ago gave up, and just try it. How about this... the shielding is actually protecting nearby digital interconnects that are actually downstream from the streamer from the power cords magnetic field? Or... who knows what else. It is not day and night, but is noticable.

A line level cable, analog out to pre/receiver, will allow you to hear differences in conductors, shielding, and connectors. I have repurposed four fairly expensive Spdif cables at this spot, each cable had their own individual sound characteristics.  I have never heard much of a difference swapping good quality cables from pre/receiver to a powered sub.

As long as cable is not picking up noise, as was stated above there won't be a significant difference. A better power cable and isolating it from the floor will make a bigger difference.

A line level cable, analog out to pre/receiver, will allow you to hear differences in conductors, shielding, and connectors. I have repurposed four fairly expensive Spdif cables at this spot, each cable had their own individual sound characteristics. I have never heard much of a difference swapping good quality cables from pre/receiver to a powered sub.

Please don’t write things like "pre/receiver" without clarification. No one should ever give the impression of a receiver being equivalent to a pre-amp. Door-stop/receiver, boat-anchor/receiver, POC/receiver, even POS/receiver, are the preferred terms.