@ johnh
Thank you for your fantastic post. Surely this type of post with so much personal experience with a good number of the most relevant currently produced amps is literally the definition of advice that "money can't buy." No pro review I've ever read (that I can think of) has so much valuable info for direct comparison.
Amir @ Audio Science Review has good test gear and has tested the Purifi. Purifi tests at the very highest level as does an amp I referred to and owned. Oh, if we could only read test results and make purchases based solely on these tests! But we can't because I owned one of those amps and Ralph's class D is at least 1.5 to 2 clear steps up the food chain in audio performance. (Maybe Ralph's class D would test similarly but I won't be surprised if it does not.)
I recently had here a superb $40k DAC and pair of class A $60k/pr mono blocks. I know the designer, who told me personally that he could improve the DAC's static test specs but would not because it would degrade its audio and musical performance.