I was going to stay out of further comments to this post but I can't help myself. My fundamental problem with this approach is the use of an isolation transformer for noise suppression in an audio system. I do use isolation transformers but for the purpose of safety when I am working inside electronic equipment. If I'm coming off the isolated side and I accidentally come in contact with one of the AC leads and ground I won't get killed. Also when using test equipment like an oscilloscope, the shield side of the probe which connects to the shell of the BNC connector is not hot in relation to earth ground.
An isolation transformer can provide some noise immunity because it has leakage inductance which limits the bandwidth of high frequency signals it will pass from primary to secondary. Also if the secondary is truly isolated from utility power ground loops are minimized. However, once you ground any of the secondary to earth ground you have a potential ground loop path from the "isolated" side to utility ground and neutral.
In my opinion, there are two main things that can provide noise rejection in an audio setup. The first deals with ground loops and is to make sure that all the AC power to all your audio devices, assuming they are 120 volts, comes off the same breaker that is dedicated only to the audio system. The noise that can creep into the system when you work off both sides of the split phase coming into your house is eliminated. Second, for RF and other transient noise carried on the lines, a commercial grade noise filter provides a lot of rejection far more than you will ever get from an isolation transformer. Then the most important ground is the one that runs from the ground connection on the filter and a good system ground. For a long time my go to filter has been one from Corcom. Here is a link:
https://www.newark.com/corcom-te-connec ... dp/52K3304It has multiple stages of line to line and line to ground filtering. This particular model is rated at 20 amps. There are smaller filters but they should have all the filtration mechanisms as this one. Most smaller ones don't. Here is a circuit diagram:
The advantage of this is that your AC supply is not limited by the capacity of the transformer which could limit performance and you have the safety (assuming your house wiring is to code) of working with standard utility power and approved grounding mechanisms.
In reality, all of these are band aids and there is no substitute for good power supply design in your equipment. However, unless you are building all your own stuff, what I have mentioned, in my not so humble opinion is the best way to go. Ok, now you can start throwing bricks.