It does not matter that Levinson used a bunch of air core coils (one thing does not make a whole).......what matters is the sound.I did not say that it was the idea of series'd air core coil output filters that ML used to get a steeper roll off as not to give phase shift down into the audio bad that made it sound bad.
The fact that a big company like Mark Levinson knew that it is a problem with Class-D, as this phase shift graph from output filters shows (red) https://ibb.co/vvwzGV5
That's why it's seems only fixable by moving the switching frequency and filters way up higher so there's no effect of phase integrity down into the audio band, and the only way to do this is move the switching frequency up much higher to 1.5mhz and the filter as Technics did with the SE-R1 and hopefully with the SU-R1000 also.
And you can't fix it but throwing "more global feedback" at it, as that is a sound destroyer in itself. The only way is the > 1.5mhz switching frequency, so the filter can do it's job without introducing phase problems down into the audio band.