I had thought that by "black" background we mean a lower noise floor, but I think David is pointing out that there is a distinction and difference between the two. In live events, the background is almost never "black". It can be very quiet accentuating the contrast between sound and silence which increases the sense of dynamics and clarity/detail. I hear this at Boston Symphony Hall and in most studio recordings. But I also think I understand what David means when he writes that there is a background atmosphere or ambiance which one does not want to obscure with a veil that covers over these subtle spacial cues and sense of atmosphere - that which defines the performance space. A quality or black background that a component or tweak imposes universally on all recordings is not good if one wants to understand what the recording actually sounds like. And in this sense, since there is a unique quality to each recording venue, if a tweak or system makes them all sound the same or similar, the system has moved away from sounding natural and or transparent.
So, if I understand David correctly, a system can not sound both transparent to the recording or source and also have a similar black velvety background on every recording. A system can have a lower noise floor with the introduction of a new component, but that is not the same as a blacker background. Most tweaks add a coloration of some kind, so they can make a system sound as if it has a blacker background but not more natural or transparent to the recording. And more natural is not a coloration which makes every recording sound the same but a transparency that makes the best recordings sound very real.
Since this is a thread about a tweak, I presume those who use such tweaks are trying to get a sound which is more pleasing to them. What if some of these tweaks make a system sound more natural to the listener? Is that not a good thing, or do all tweaks add a coloration to the sound which prevent the system from sounding natural, or more real?
The question I have though is does a natural sounding system impose a universal character on all recordings or is it another way of saying that the system is transparent, imposes very little on the recording, and therefore resembles the sound of real instruments in real spaces on the best recordings?
At least this is how I understand David's posts. If I am mistaken, I welcome David's corrections and input.