Dedicated 20 amp circuit - Electrician laughed!

Ah, hem, a theory once proved is a law. You know, like the expansion of the universe, theory of General Relativity, Einstein’s theory of gravitation, the speed of light = c, E=mc^2 Things of that nature.

In the 1850s, Ohm’s law was known as such and was widely considered proved, and alternatives, such as "Barlow’s law", were discredited, in terms of real applications to telegraph system design, as discussed by Samuel F. B. Morse in 1855.[13]

The electron was discovered in 1897 by J. J. Thomson, and it was quickly realized that it is the particle (charge carrier) that carries electric currents in electric circuits. In 1900 the first (classical) model of electrical conduction, the Drude model, was proposed by Paul Drude, which finally gave a scientific explanation for Ohm’s law. In this model, a solid conductor consists of a stationary lattice of atoms (ions), with conduction electrons moving randomly in it. A voltage across a conductor causes an electric field, which accelerates the electrons in the direction of the electric field, causing a drift of electrons which is the electric current. However the electrons collide with and scatter off of the atoms, which randomizes their motion, thus converting the kinetic energy added to the electron by the field to heat(thermal energy). Using statistical distributions, it can be shown that the average drift velocity of the electrons, and thus the current, is proportional to the electric field, and thus the voltage, over a wide range of voltages.

Theories are never proved. Ohms law holds in a ohmic device. Calling it a "law" was simply a convention it could have been called Ohms obersvation or Ohms theory. 

http://oer2go.org/mods/en-boundless/www.boundless.com/physics/definition/ohmic/index.html

I have three dedicated lines in my sound room.  I’m running two Krell EV 600 monoblocks. Each has its own 20 amp circuit, with hospital grade outlets and 10 gauge wire. I’ve never tripped the breakers, but am more cautious with my hearing than I used to be. The rest of my room is on another dedicated 20 amp circuit.  All are wired to the same side buss. I however do not have a dedicated ground.  I’ve never experience any ground loops or hum and am very thankful. 

He’s Not really correct.  I’ve had huge improvements going to a dedicated circuit when OTHER ITEMS on that same circuit are noisy.  Fluorescent lights, hair dryers, microwaves and vacuum cleaners are quite noisy and will cause visual (TV-projector) mouse as well as audible noise.  A dedicated circuit can help in those cases.

A good wiring technique (USA) is to put the noisy items on one “leg” in the electrical panel and keep the audio items on the other “leg”.  (In the USA, boxes are fed with dual 120V wires or “legs”; most circuits only use one, unless they are a 220V circuit.  Air conditioners, stoves, air compressors, welders are 220V and all else is 110).  The wiring strategy is to keep bathroom circuits (hair dryers)  and living room / bedroom / hallway circuits (vacuum cleaners) and buzzy lighting circuits (fluorescent) on one leg and audio on the other.

His assumption in needing to run a new ground is based on issues with ground loops.  If the length of wiring on all audio circuits to the box is the same, ground loops are often avoided until you introduce coaxial cable into the mix.  Use isolators if that happens.  RCA cables (subwoofers) also cause ground loops; in that case consider higher-end gear with XLR interconnects or use isolators on the sub RCA’s.

Also, high end gear can have huge current draw, especially with Class A gear.  Sharing circuits can cause tripped breakers or blown fuses.  If your lights dim and flicker during loud passages, you need a dedicated circuit.