@Fosom, I would be interested in your considerations with regard to Ballanced Power between wall mains and system.
Balanced transformers help to phase cancel a minor amount of noise. The isolation that they also have is a bigger benefit. From the perspective of a component it is good and bad for the transformer in that inner and outer side of the windings can have different sounds due to leakage to ground. If you're on single phase unbalanced you can literally just switch hot&neutral and see which sounds better - it's that easy to hear. And by switch I don't mean mess with AC wiring of the home or power cable, I do mean inside the equipment to correctly maintain safety.
As much as these transformers help, they do create some other issues. Parasitics go unnoticed, for one - by everyone I've ever seen. They also don't do anything to help keep the secondary side (stereo equipment side) from interacting with each other. I personally wouldn't get one because it just compounds potential problems, but that doesn't mean it isn't possible to come out better when they're addressed.
For any and all of them I highly recommend my Lillies - which the special variation for balanced transformers does work against parasitics. The ones that go in the breaker box will help maintain a complex impedance that is friendly towards the primaries, so they can act as intended in the transformer. Depending on distance from the stereo I may even recommend further corrective measures to make sure you're not losing as much as you're benefiting. Some stereos with a long distance from the stereo to the transformer may have much worse issues, but ironically be more treatable. The small balanced ones that are only a short power cord to the equipment cannot be treated easily if they exhibit any issues because you have two low impedances that will dominate a lot of corrective measures. The only way to work with that is basically to insert a conditioner of a sort between the two.
I hope that gives you a snippet of what runs through me head when talking about them. It can get more complicated like with looking at multiple winding secondary outputs, and addressing worries about capacitance between them.