“Black background” — What really contributes to this phenomenon?

In the digital domain it’s all about inherent noise contaminating the signal. The best designs today take great pains in power supply design to address this, and it not only makes the contrast between quiet and music more distinct, it allows one to hear deeper into the mix so to speak.

Audioquest Niagara system with appropriately matched power cords did it here. Another step you can take is use sheet copper to maintain a barrier between analogue and digital components. In my case I use copper sheeting under my pre-amp and FM tuner. Streamer is directly below the tuner and my Benchmark DAC is right below the pre-amp. I also use Pearl tube coolers and solder a wire I can take to ground to them to drain off any RFI or EMI that may effect tube performance + the cooler has the tube’s head running 20 - 25 degrees cooler for longer life.

@redwoodaudio google ac filter chokes - many audio manufacturers use them - in the old days Counterpoint used them. Hammond makes them and so does Plitron.  In some equipment you can install a choke where the AC lines come into a unit, etc.

Peter