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.
Rubbish. Bruno Putzey's UcD module, which is quite old at this point (and predates NCore and Hypex), has less than 1 degree of phase shift at 20KHz. It switches at 400KHz and is self-oscillating, with about 40dB of feedback.