HIGH Quality Electric Service Panel

You are correct; the greatest difference is heard when running these lines to AMPs, especially big wattage amps.   However, when I replaced my dedicated 12awg  line with the 6awg (in my previous room) for my 'front end' pre, phono, and DAC i got positive results; not as dramatic as with the dedicated amp life lines but still an improvement.

stickman451

... you have to junction box the 8 0r 6 down to 10 to fit the receptacle ...

You can do that, or you can use a pigtail. Either is acceptable.

I ran 4 dedicated 10awg romex to 4x4(2 duplex 20a outlets)boxes every 4 feet in my theater/2 channel room and it worked without issue.
But then again I don't spend on snake oil either.