Just my 2 cents.
It sounds like you have things pretty well in hand. Though fellow Agoner's will have opinions/recommendations, perhaps you should consult a local high end dealer or installer. So much of this has to pass local codes, so someone knowledgeable about local codes would be the best source of information.
Just my 2 cents.
gdnrbob- There are a couple Austinites here who have done systems- I’ll try to reach out to them as well. Thanks.
Eric- already have Quad IIs that were part of my personal "museum" (e.g. non-working display items) that are in the capable hands of Bill Thalmann at Music Technology who is going to restore them, along with an McI MX110 preamp/tuner I bought and is now doing the Krebs update to my old SP-10 turntable for the "vintage" system.
Domestic isolation transformers are a little noisy (I use a Torus WM-75BAL which is a 9000VA transformer) but not too bad. Mine is in an adjacent storage room but the door to that room is double thickness and soundproofed. The main fuse box is in the next room (the garage) thus all runs are kept short. The Torus product is one I can highly recommend.
I also recommend the dealer I worked with - Nyal Mellor at Acoustic Frontiers, he is very knowledgeable and able to source anything you need for this sort of project
lloyd- yes, aware of that. I had soundproofed the last closet where my air compressor and a stand alone isolation transformer were located, but point is taken. If the electrical/inspector allowed the transformer/panel to be located in un-air conditioned attic space, it would be further removed, not so hard to work in, but the Texas heat can’t be good for it.
Folk- indeed. I already have a big Equi=Tech balanced power wall cabinet sitting in storage, I was planning to see if I could use that in the separate building. What I need to bore down on is basically a naked isolation transformer that would be installed in an appropriate generic cabinet as part of this in-house set up. I’m trying to avoid going full on crazy, but still within code and a reasonable budget, since it is an interim step to a separate building, where I will install either the Equi=Tech I have or something along the lines of what you linked to----
Every time we’ve bought a new home, there are expenses that are ongoing and considerable to get the place to the level we want it. I eventually go numb, and get to a point where I refer to the cost in "units" rather than dollars. It makes it easier.... :)
Echoing the above, seems like you have a really good start. Regarding the dedicated lines and interference, running the lines seprately and not bundled is of course a good thing to do. You may also want to consider running shielded 10g Romex - I had pretty good success with it (had it cryo treated by Audio Excellnce as well). I have also had success with Cardas in wall cabling as well.
Also, something to consider - the best step I have ever made in reducing noise via the electrical setup is using a 10' chemical grounding rod buried in bentonite clay - massive improvement for a reasonable cost in view of high end audio. There may be some hassle in rewiring it to you new audio outbuilding when completed, but I would suggest it is worth it.
Best of luck.
Oh, and if you have any interest in Hard Country, Western Swing, etc. music Bill, I heartily recommend Austin’s The Cornell Hurd Band. Cornell is an old friend of mine who has been playing in the Austin Honky Tonks since moving there in the late 70’s. He’s a great songwriter, having tunes of his recorded by Junior Brown and The Skeletons (the fantastic band from Springfield Missouri, whose fans include Nick Lowe) amongst others.
Yup Bill, Country/Hillbilly without any trace of Pop, Rock, or other derivatives mixed in to make it more palatable to those who distain the "nasal twang" of the real stuff. You know, Hank Williams, Lefty Frizzell, Ray Price, Hank Snow, Ernest Tubb, Roy Acuff, Bill Monroe, Bob Wills, Moon Mullican, Pee Wee King, Red Foley, Hank Thompson, Johnny Bond, The Delmore Brothers, Don Gibson, Jimmie Rodgers, The Carter Family, Johnny Cash, Merle Haggard, Buck Owens, Johnny Horton, Sonny James, Slim Whitman, Marty Robbins, Tennessee Ernie Ford, Stonewall Jackson, Ferkin Husky, George Jones, Tammy Wynette, Kitty Wells, Patsy Cline, Loretta Lynn, Wanda Jackson, and hundreds of others.
Cornell really knows his stuff, writes great songs, and always has a top-notch band featuring fiddle, pedal steel, piano, Telecaster guitar, bass, and drums. Plus, he’s a heck of an entertainer, with a wit the equal of Dan Hicks.