I’ve done several rooms over the years when we moved households. This latest was in an 1880’s Texas Gothic (Victorian) which had a full restoration in 2004. Almost the entire first floor, (with the exception of the kitchen) was original, including all woodwork, transom windows, shutters, etc. The listening room, upstairs is modern, and loft-like.
I had a couple of phases of electrical work done. First, I had a commercial electrician go over the entire electrical system starting at the meter- which the power company pulled to inspect the meter block. A feed was run to a sub panel and since I had planned to install a large iso transformer, the feed continued upstairs- all done in 4 gauge. That led to a service panel for the music room- copper buss bar--and 10 gauge dedicated lines. System sounded a little bright for a couple weeks- wired with a junction box where the iso transformer was to be located (it was built to order).
When it was installed, I cannot say it made a dramatic difference in sound, but the system was dead quiet. I use 104db efficient horns and you can hear grounding anomalies among components, and any noise on the line. Even though I am very close to downtown, the system is far quieter than it was in NY, along the Hudson, where the infrastructure was old.
Next phase was installing a whole house generator. I wanted to avoid the problem Fremer complained about- that the automatic transfer switch, which is filled with semiconductors- made his system sound terrible. I figured there was a Code compliant way to wire the system so that it was powered from the service entrance before the ATS/Generator. I called on Rex, who helped Fremer re-do his system. Rex can do this remotely with drawings over the phone for modest cost. The electrician installed an ATS with its own breaker box--and only those appliances that are wired directly to the ATS breakers are supported by the generator. The hi-fi stayed on the main service panel, thus not connected to the ATS. I probably eliminated 1/2 the breakers on the main panel, everything got checked and tightened. The system sounds better than ever. I attribute that to fewer breakers on the main panel and having everything tightened; put in a fresh grounding block (I think they are zinc) that ties main ground to other utilities like phone and cable-I have neither, but do have Google Fiber here).
I like to use commercial electricians b/c they are used to dealing with big equipment, heavier loads, etc. The grounds all tie back to the main household ground- a Ufer which is essentially rebar in the concrete foundation.
Think carefully about receptacle layout for future needs, especially if you are breaking drywall to install the power lines. It’s a little messy-- I had this done before the system was uncrated and installed. Everything got patched and painted first.
You don’t have to go to the lengths I did-- FWIW, I use the last of the Porter Ports Albert had. I did have a copper ground bar installed near the front end of the system (also tied to the household ground) in case I needed a verified "ground" for some additional equipment.
The digital side (modest) runs off the regular household wiring- there is a power conditioner on that circuit, but not on the main system or analog side. There is a surge board in the iso transformer and I bought a new whole house surge- the Siemens (yikes the price on that doubled in the last couple years), but all good.
Most electricians are not audiophiles- sometimes you’ll find a commercial electrician that has done work in stadiums or other venues. Those guys are used to the demands audiophile place on their work. Get several quotes and find an electrician that does both commercial and residential. That’s where I’ve gotten my best results.
Good luck. @Jea48, a member here, is very knowledgeable on NEC but Code can vary (more requirements than national) based on location. The National Code is a minimum standard. Overkill is not a bad thing.