High quality in-wall UL-C2 rated 10-gauge A/C wiring ?

@jea48 point is well taken. In Southern CA I had no issues having the jacketed JPS cable put in directly in wall but in Portland where (probably in retrospect in error) I had conduit installed my electrician needed to strip the SR Romex into its three constituent cables and run them separately inside the conduit. Suffice it to say consult your local code knowledgable sparky before you set off.

Romex style with two parallel conductors and the earth between them is only bested by twisted LNE in aluminum and twisted LN.

The worst is random wire in steel conduit.

see https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf p31ff.

https://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

A question for the fancy-pants fans: Electricity comes hundreds of miles, through umpteen transformers, 'suspect' cable & connectors to power meter, panel, breaker, & jack and a few feet of fancy wire is going to 'fix' it?

Not sure if my experience will help, but I recently moved to a new house and had a dedicated AC supply wired with this cable -

https://mcru.co.uk/product/mcru-10mm-shielded-mains-spur-cable/?v=69e1aafeccc5
In my previous place, I also had a dedicated supply but wired with normal romex.  Well, my system (no change before move & now) now sounds quieter with less background hash & noise, the midrange is richer and the top end resolution is better but sounds less sharp.  I need to clarify that the room is obviously different with much higher ceilings (16ft. now vs. 9ft before) but leaving that aside, there is no doubt that the sound now is much much better.Hope this helps. 

A question for the fancy-pants fans: Electricity comes hundreds of miles, through umpteen transformers, ’suspect’ cable & connectors to power meter, panel, breaker, & jack and a few feet of fancy wire is going to ’fix’ it?

Water comes all the way to your house in/through some of the worse conditions imaginable, and yet we filter it before we drink it.

Despite the red herring, it’s the condition of the power right where it enters your house/abode, be it at the junction box, or the outlet, depending on what you can afford to do, that matters. That 17,000# transformer outside your house, on your block, kind of makes moot, the whole thing about all that distance it had to travel.

A little filtering here, some better wiring there, ensures better, consistent power.

All the best,
Nonoise

Each transformer in the line adds some distortion. The neighborhood transformer couples the grunge from the neighbors on to mile line.

Filtering I understand.
What is the filtering capacity of a 2m 14ga cable?

One of the claims is better transmission.
Power lines are contaminated with DC, several 10s % HD, RF, etc.
So, the fancy cable is better able to pass the noise and grunge?!?1?!