I don't know if you have thought of this before but is your elctric supply to your system from your ring main or a dedicated supply from your box to your system alone . I have made myself a new spur with Neotech 3001 mains cable, it's fantastic stuff but expensive. It is very well shielded against RFI and mains nasties and it has made an amazing difference to my system ,no fridge clicks or transformer hum anywhere. It was the best couple of grand I have spent in a long time.
Isotek EVO3 Sigmas
I recently splurged on this power conditioner, and after a fairly lengthy back-ordered wait, it finally arrived recently. There's good news and there's bad news.
The electricity coming into the house clearly isn't great. There's a pair of built-in ovens in the kitchen, and the upper one has the control panel. Evidently, this includes some kind of transformer, as you can hear a low-level hum/buzz through the kitchen cabinetry night and day.
Likewise, the amp's transformers have a similar fairly mild hum, AND this also appears in the speakers.
The reviewer of this Isotek model in The Absolute Sound said that it tamed a mild hum in his transformers. I've also seen the youtube video with the noise-sniffer, where its insertion completely eliminates the nasties on the line.
The bad news: the hum (amp + speakers) is identical to before. On bad days, when the music falls silent, you can hear it from the listening seat. (BTW, I've already tried Audio by Van Alstine Humbuster and also Ebtech HumX, both to no avail.)
The good news: there was a distinct improvement in the presentation of the music. It was louder--I was immediately reaching for the remote control, fuller, with more body, more texture, more presence, more resonance, with sparkling highs, and particularly a great sense of ease on the fortissimo passages.
So there's the quandary. Is the good news worth 4K? Or does it go back, and I keep experimenting with Equitech, Torus, PS Audio, Audioquest, Shunyata, etc. in the perhaps futile search for a unit that actually quietens the hum?