Yet another Grounding Question-Separate 'Earth'

Whart, what is the problem (power, safety or audible) that you are trying to cure? Why do you need a separate panel? Maybe there is a simpler way.

>>By using separate or multiple grounds, the possibility exists that a short circuit may be routed away from the breaker, causing a dangerous situation.<< Only the hot side of the circut is fed through the breaker, so multiple paths back to the panel are immaterial. The current has already been through the breaker and cannot be routed away. The ground wire itself is a separate path, parallel to the neutral.

I do agree that not connecting new grounds to the exsiting panel or connecting the subpanel neutral to ground anywhere but the main panel are REALLY BAD IDEAS.

Let's talk about the underlying problem and try not to create new ones.

I hadn't been down to the basement to look at his work- here's what we have right now: a Square D subpanel is feeding off the main panel, fed by a metal insulated cable that appears to be close to an inch in diameter. No further work has been done (yet)- he will return later this week. I suspect that when he said he wired this panel in, 'upstream' of the existing box, he really meant upstream of all the existing breakers, perhaps, save for the main power breaker on the incoming service.
The ground wire out of the main box is a massive thing, looks like its multistrand, also probably an inch thick, wrapped in a light grey, rubber-type insulator.

I'll make sure I discuss these postings with him. He has done good work for us in the past, and is pretty meticulous. Perhaps he didn't mean that the ground to the subpanel would be totally isolated, and that the panel wouldn't also grounded to the main house system, but I sure heard it that way.
As to problems I'm trying to solve, well...

The room in which the hi-fi exists is already overcrowded with other equipment for the video system. My preference would be to install the audio only system in another room, but at least for now, that's not possible.
I'm pretty fanatical about the noise level in the system, and have tried myriad ways so far to reduce the noise level at idle. (As mentioned in another post, an industry guy who I respect for his technical knowledge heard the system a couple weeks ago, and scoffed at my complaint that the system was noisy).
In any event, the video system is powered by its own dedicated 240v stepdown transformer. That in turn handles the power for the various 'audio for video' amps and also supplies the juice to a big Richard Grey box which powers the projector, line doubler, and small signal video stuff.

I want the audio system totally isolated from that, and I'm moving the audio equipment (other than the speakers) to another area of the room --partly to get it away from my ears, and partly because the compressor for the Air Line arm can then be stashed in its own little room, isolated from the listening environment.

In doing this, I just want to make sure I have the best possible AC feeding the system. The current demands made by the system are modest. While I am currently using Shunyata Hydras, I'd also like to hook up without them, and see what the difference is. At present, the other outlets in the room are not 'dedicated' and are part of the standard electrical system that was installed in the room about 5-6 years ago, when the upper floors of the house were substantially renovated.

ps- house has 200 amp service, all upgraded about 5-6 years ago when the house was massively upgraded by the prior owner.

Whart,
>>"house has 200 amp service."<<
>>>>>>

I assume the 200 amp main breaker shares the same panel enclosure as the branch circuit breakers. Is that correct?
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>>"fed by a metal insulated cable that appears to be close to an inch in diameter."<<
>>>>>>>>>>

From your description the wiring assembly is MC cable. 1" in diameter, probably 4 #6awg THHN conductors. Maybe 5 conductors if the MC is Hospital Grade. I am just assuming the sub panel will be a 120/240 volt panel. 2 Hot conductors, 1 neutral conductor and 1 equipment grounding conductor. Wire ampacity rating of 60 amps.
Is that correct?
At the main electrical panel, the electrician will install a 2pole 60 amp breaker for overcurrent/short circuit protection for the new sub panel feeder and sub panel bus bars. The 2 conductors of the MC cable, usually black and red, intended for the 2 Hot conductors will connect to the 2pole 60A breaker. The white (neutral) and green (equipment grounding conductor) will both connect to the neutral/ground bar. At the sub panel the neutral conductor will connect to the isolated neutral bar and the equipment grounding conductor to a separate ground bar bonded to the panel enclosure.

What type of branch circuit wiring will the electrician be installing? What brand of receptacles are you going to use?
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EMI noise.
Just curious why are you not just installing another isolation transformer with electrostatic shielding and a new panel to feed your audio equipment branch circuits. Usually a sub panel is installed because of a lack of spare breaker spaces in the main electrical panel or the audio branch circuits conductor are very long and ground loop problems exist.

OK, not to add to the confusion, but to answer the questions:

We have 200 amp service, goes into a main panel with one big breaker, littered with all kinds of smaller 15 and 20 amp breakers (box is quite full), and an existing subpanel that appears to be set up for some of the kitchen appliances.
The new subpanel is a 100 amp box, set up right now with 3 Square D 20 amp breakers. I'll check to see if he installed a 60 amp breaker in the main panel to support this new subpanel.

It was my intention to have him set up a number of 20 amp dedicated lines from this new subpanel, strictly for the audio-only system, and rather than have him ground the receptacles at each wall box, to run separate ground wires back to the subpanel for each- not daisy chaining the receptacles to each other. I have ordinarily used Hubbell Hospital Grade receptacles- only because of habit, and because i know Bill Hubbell, and figure his trust fund needs the money (He is a serious car junkie).

The run from the panels up to the room is easily 75-100 ft., depending on routing.
The only reason I hadn't considered another transformer for this system is that the one currently used in the video system is located in the room, inside one of the Mid-Atlantic racks, and I can hear it hum at idle, when all the video equipment is shut off. (When the video system is on, the fan noise masks that). I suppose one could set up an isolation transformer down in the basement, near the panels, but would that defeat the purpose if the outputs of the transformer then have to make that long run? Apologies in advance for my ignorance.