I believe the best performance and SQ will be using a linear power supply
That’s exactly what I did in the 2nd system with my Hypex NC500 monoblocks (same as BelCanto Reference-600 monoblocks). Two things I did that took them to another level, I now have a massive linear supply and the other was when I also completely bypass the Hypex modules input gain stage, because my MSB Discrete R2R DAC has up 7.5Vpp variable output and can drive each of the NC500 poweramps balanced in stage itself direct.
Would you rather have your 1.5MHz and lesser SQYes defiantly the 1.5mhz or more switching speed "and better sound quality" it brings. Because the 70 degrees of phase shift in the upper mids/highs https://ibb.co/2thS6y2 on Class-D’s will then be almost reduced to 0, like good linear amps that have FR’s out to 200khz and because of that they also have almost 0 phase shift in the audio band
Cheers George