Which Class D Amplifier? PS Audio, Ghent, Nord, Merrill or other???

Try ClassD Audio. Excellent product and value. Tom, the owner is great to work with.
http://classdaudio.com/

slimpikins

I haave owned 6+ class Ds oer the last decade, and owned a Parasound A23. I MHO the Audio Alchemy class D comes closest in warmth but is much more open

ATI makes a very good class D amp. They have a linear power supply, sound great, and don't cost an arm and a leg. 7 year warranty.
https://www.ati-amp.com/AT52XNC.php

What’s the failure rate among various audiophile Class D amps? Is it higher than class A/B? Has it improved over time? 

Bel Canto REF600M monoblocks. I never heard a class D amp I liked until I heard these and they are superior to just about everything on the market, and an absolute bargain at less than $5K. No harshness, no digital edge, no noise, no whitish coloration, no tubey softness..... just right. Exceptional dynamics, resolution, damping. And they can drive any speakers with ease. Plus they’re energy efficient.