AC Dedicated Line

That way, when big crescendos emerge, you know full current is still available to the rest of the system.

Not so. Full current is supplied by the PSU caps. The wall only supplies current when the cap voltage is lower than the line voltage plus 1 diode drop. See Rod Elliot's http://sound.whsites.net/power-supplies.htm and http://sound.whsites.net/power-supplies.htm#s51 in particular.

In the case of any peak that is out of sync with the line voltage the line supplies ZERO current.

In case of any frequency below the line frequency, the line only supplies current for a portion of the cycle.

In the case of frequencies above the line frequency, the line only supplies current for some of the frequency.

The increase in headroom for over size wiring amounts to about 0.25db. See https://forum.audiogon.com/discussions/headroom-loss-for-1600w-on-14ga-120v

ieales

Not so. Full current is supplied by the PSU caps.

You’re either deliberately splitting hairs here, or just not reading carefully. Obviously, the PSU caps can’t supply current to components not connected to it, but which are connected to other dedicated lines and power supplies. Those components are indeed powered by their individual caps which are charged by ... the line. They can’t be charged by the line if it has run out of current - hence the advantage of dedicated lines. (And a reason to not power all components from the same leg - but that’s a separate and debatable issue.)

If the line has run out of current, the breaker has tripped. AGAIN, cap charging is almost completely asynchronous to the music. 

In the studio, we had a stack 4 of Bryston 3B for the tri-amped mains. Dual woofer, 1 mid & 1 tweet. 8 amplifiers. All on one 20A circuit. In LA, we had frequent brownouts and full outs. When power was restored, EVERYTHING came on at once. If the breaker doesn't blow when powering them all on at the same time, the line can handle the load.

In round numbers:
A 200W amplifier supply is 40V, 8 200w amplifiers could supply 40A TOTAL into 8Ω. On 120V, that is a 3:1 transformer turns ratio. So a 20A circuit could supply ≈120A to the amplifiers. Add in the FACT that a 20A breaker can supply peaks of several times 20A. A Class B resistive breaker has a 3-5x multiple of rated capacity for a couple of seconds. THAT'S 500A IN THE AMPLIFIER!!! See  https://www.c3controls.com/blog/understanding-trip-curves/ 

The advantage of one circuit is earth reference with improperly designed gear, which IMO is far more prevalent in HiFi that properly designed. Balanced gear can have some immunity, but unbalanced could be a nightmare on multiple circuits.

And for the 999th time, the power loss, even at worst case conditions is under 1db. For that loss to occur, the peak must be in sync with the line frequency.

The ground is a true earth ground made by the electrician that wired your home. It is a 6' copper rod driven in the ground and connected to your electrical panel with a large single conductor to the ground bar in your service panel.

Very False.

Many locales permit Ufer grounding.
https://en.wikipedia.org/wiki/Ufer_ground and https://www.ecmag.com/section/codes-standards/what-ufer-ground-concrete-encased-grounding-electrodes

Ufer efficacy, like most things audio, is contentious. Concrete resistivity varies dramatically [≈10^4]. Factor in construction vagaries, rebar fabrication code compliance, local soil and the likelihood of two installation being identical is slim.

Any ground rod MUST tie to the panel neutral. Any circuits that have the safety ground connected to 'earth rod' only are illegal and dangerous. The earth [dirt] is high impedance and insufficient breaker trip current will flow when an equipment fault makes the chassis live.

How many 'AC Dedicated Lines' are actually worse from using incorrect safety grounds and steel conduit and random wrap individual LNE than the plain old Romex it replaced?

I didn’t consider ground loops, so I will interconnect both ground bars on the entrance or I will keep one single ground bar for all circuits, new and old.

Terminology: Ground ROD is in the earth and connects to the Panel Neutral BAR which connects to Transformer Neutral.

There’s more to ground rods than just sticking a piece of copper in the ground.

Adding two rods could reduce their efficacy in the event of a lightning strike, their primary purpose.

If materials differ, you could set up a galvanic cell which would eat one away. Ditto if perchance soil & moisture conditions differ dramatically at the two locations. Unlikely in a home installation but not outside the realm of possibility.

The 3rd pin is a secondary SAFETY path to return fault current to the transformer neutral to ensure enough current flows to trip the breaker. If you don’t return the 3rd pin to the transformer neutral YOUR SYSTEM IS LETHAL!