FWIW, I seem to have had the best luck over the years with Square D brand products and the worst luck with Federal Pacific.  If it were me I would install the new panel with a new ground rod and then plan out your breakers.

The box will have two 120 volt legs.  I would take a look at all the 120 volt appliances in the house, anything with a motor or heating element and situate all of those loads on one leg that we can now refer to as the noisy leg.  Put everything else on the other leg.  We'll call that the quiet leg.

Place your audio room breaker (20 amps) as the first breaker on the quiet leg.

Place your 240 volt 2-pole breakers at the very bottom of the panel.

Use 10 gauge romex wire (10-2 with Ground) and run a continuous length from the breaker box to the outlet in your listening room.  Use hospital grade outlets.

Yes, the 10 gauge is rated for 30 amps, but you will only be using it for a 20 amp circuit, of which you will never probably draw more than 5 or 10 amps.

If you get involved with the "audiophile" in-wall AC cable you've mentioned, I'll strangle you with it.

Steve

There ya go, no need to search further, you got it from the one who knows. Plus, I’m still chuckling at his last sentence...you won’t get any better advice...anywhere.

Best,
Scott

Steve nailed it!  I had to laugh at the audiophile wire comment, especially since I used Zen Styx type 10AWG and 8AWG wire for two hospital grade outlets. LOL

That said, I'm sure it was overkill - just keep the resistance low (hence 10AWG) and your connections firm (Hospital Grade Outlets)

Since you're having a new panel put in, see if the installer can measure your resistance to ground. The lower you can get your ground, the easier it will be for noise to be dumped to ground (path of lease resistance, right!).  National Electrical Code (NEC) is very broad on this subject as NEC is for safety, not quality of ground.  So the installer might say "it's good enough", but it can't hurt to exceed the safety spec for *quality*.  NEC spec is 25ohm if I recall, but IEEE spec is like 5ohm. When I finally got my house sorted out I was at like 1.5 to 2.5 ohm depending on how moist the soil is.

https://www.ecmweb.com/sites/ecmweb.com/files/uploads/2014/03/4346628a_en_EarthG...

Whether carrying power or signal inside amps, in ICs, in speaker cables, or in power cords, I can't recall a wire change that was not noticeable enough to make a choice valid for me. Differences in purities and drawing methods of silvers and coppers, different dielectrics, geometry, different gauges...so far, all have been audible enough to matter to me.

That said, I have not experimented with in-wall wires. But hearing from a few folks with good ears who have explored this over time, like Steve, they find 10 gauge Romex is good, especially for the money! Seems wire and cable geometry matters, but perhaps less in-wall than after the receptacle. I Don't know from experience, but with these tips, I am inclined to go with 10 gauge Romex.

I have also heard from folks with good perception that cyro'd Romex is audibly better. I have liked everything I have had cryo'd, so I am considering some 10/2 w/ground from audioexcellenceaz.com, who has a lot of cryo experience, will pick up stock rolls of the wire locally, and cryo whatever roll length needed. It seems he will also cryo dedicated breakers. He is the developer for the Cable Cooker, and if desired, he will "cook" the cable.

Not sure, but I am thinking of two runs with two separate receptacles in order to separate the amps from digital.

Any thoughts?

Mains off and voltage checked, looking in my panel today to see what breakers I will need, I found the older Square D breakers have a sort of bracket clip that connects across the buss with a spring tension. Many seemed a little too loose, so I decided to pull them one-by-one and squeeze the connectors together a bit. Grabbing the buss with better connections, I think I am hearing some increased clarity, solidity and ease with the system. It seems everything is a little quieter, system, refrigerator, air filter...

Finally, I have not tried a lot of receptacles, but have found meaningful differences. For better flow and more transparent sound, I liked the a Hospital grade receptacle I used for several years better than the one that was here. But testing others for a power conditioner maker, I found several I liked quite a bit better than the hospital grade and some not that expensive. My favorite now is a Mapleshade, I think old stock, light construction, with ceramic wire nuts and a maple faceplate, costing something like $70.

Not that I'm a doubter but did you get to run the system much on the old outlet?  Just wondering if you're new place has cleaner power in general.

Wow, that's a LOT of stuff on the line.  I worry about my line having an extra (unused) hospital grade outlet and a couple small curio lights above the amps!  You definitely did the right thing.

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I would say that could be a great idea provided the computer is optically de-coupled from the analog audio system.

Steve

No, your dedicated line for the audio system should be used by all of your audio components, and ideally all plugged into the same group of duplex receptacles to prevent ground loops.

Steve

Plus+1 to everything the Zenmaster has recommended.  +1 on the Square D products too.  I had the opportunity to do nearly all the things he recommended above when we had our house built.  I have since then, with a remodel, also rearranged breakers/circuits in the panel like he advises.
If you have a dedicated line, connected in the main breaker panel as Steve directed, and plug all your components into that same circuit, your chances of having problems with noise and ground loops is drastically reduced.  Reduced to the point, that if you do have a hum issue, it's probably one of your components(or interconnects/connections) and not an issue with the power in your house.
I have several different pairs of single full-range driver, high efficiency speakers, ranging from 95ish DB to a little over 100db.  I use a Decware amp to drive them.  And a tube preamp most of the time.  I have to put my ear nearly against the cone to hear any noise - now that's quiet!!  All of this contributes to my system being more resolute than any of my buddies systems.  You will not regret the little extra effort and costs required to get good clean power to your audio components.