My NAD 3020 D proves your Class D tropes are wrong

@jwl244 I am curious in your opinion and others in this forum...Is one possible reason we lean away from class D because of its distortion profile or lack thereof? My understanding with the best class D and purifi products distortion is really low.

Possibly. I find dedicated solid state class-A amp owners may tend to be more forgiving of traditional Class-D sound thinking about "heat" and "weight", and yet Tube amp owners not as much at first (maybe liking some distortion, with 2nd and 3rd order harmonics); however some hard-core tube amp owners may like the idea of rotating in another amp to spare their prized tubes on rotation, or like the idea of less heat over the hotter months of the year. Reasoning and conditions vary by individuals we can suspect. All a guess, I’m simply trying different things when I can.

And, to your first point, silly me went over to the Audio Science Review (ASR) forum and started asking if "anyone" had tried pairing up a really good tube preamp with the NAD C298 Purify module based amp. Quickly realized all measurement extremists over there, few wanting to engage into "sound" discussion or anything with higher distortion. Felt like a single alien against an army of thousands of pure scientists only focusing on measurement. Stupid me, I still want to try a really good 6SN7 tube preamp in front of a NAD c298 class-D amp just to see what happens.

A few great measuring amps and ruler flat speakers I’ve heard in my system were some of the most boring and non-engaging to my ears. Blame my room and/or blame my ears, the difference was notable to my ears. I like a little distortion in the right places.

Distortion: Something on that same type wavelength. I evaluated an ultra high-end solid state DAC a few years back, 125db SNR, amazing build quality, amazingly huge sound stage. Clear, smooth, deep in detail, yet it was one of the more fatiguing and un-engaging pieces of equipment in my particular system. Was kinda shocked. "All the notes, none of the music". Then one month later swapped back to my more distorted R-2R ladder DAC with a musically distorting tube and all the "music" and engaging layered three dimensional sound returned. Wallah, back to listening to music instead of listening to components. Recently heard a very nice higher $ class-D ice module based amp at a buddies house. He left it on for 3 days before I got there. I’m not sure if we agreed it was missing some of the harmonics. He later went with a dual tube R2R DAC, and it helped some however it is not able to produce a layered and 3-diminensional sound that I’m more use to. Smooth, somewhat musical, and 2-D at best. I think I’ve listened to class-a and tubes for too long and we all formulate our opinions on what sound good to us or perhaps leaning more towards the familiar sounds we started with or grew up with.

If you follow Paul @ PSAudio, hard core solid state guy for several decades since his time at Krell, recently accepting hybrid tube front-end BHK designs paired into their mosfet amps. Who’d a thunk, it happened. Then he opened up to Class-D. Who’d a thunk, it happened again. Even Paul reports publicly Class-D is going to be something to recon with (even more so), with added designs and development "over the next 5 years". I’m not totally "there" yet willing to continue to experiment as options evolve a bit more. Its exciting to see more rapid progress past 2-3 years with class-D, and eventually I plan to own a good Class-D amp. Looking for a great "keeper".  AGD has done some neat things... Also, kinda waiting for the right sounding hybrid design to surface. I’m betting we’ll see more coming from purist SS & Tube manufactures, realizing they have no choice now but to accept Class-D like PS Audio did, and doing well at it.

Class D is used in most powered subs which is not to say it can produce high frequency well. But i do have a harman kardon receiver that is class D in one of my smaller systems and does very well with movies. If you want good clean power spend the money and get a mcintosh.

Class D amps have traveled quite a long journey over 25+ years.
Surely, there has been a lot of focus on improving the technology.
I have been a dedicated tube guy for most on the past 50 years into this hobby. About to turn 68, got my first system when I went away to school at 18. BTW- it was a Pacific Stereo $199 special with the original Lenco TT. 25, or so, years ago I was thrilled with the Spectron, think it was, Class D amp. Believe it was the first. And even then I was excellent and had great qualities beyond tubes.
Noticed in the “recommended components” recently was the $50K Solution 501 mono blocks. Believe they are a type of Class D (switching power supply) with AB output. Has anyone heard them?
They must be pretty special...

And, to your first point, silly me went over to the Audio Science Review (ASR) forum and started asking if "anyone" had tried pairing up a really good tube preamp with the NAD C298 Purify module based amp. Quickly realized all measurement extremists over there, few wanting to engage into "sound" discussion or anything with higher distortion.

And that is the difference between a technician and a scientist.  With the exception of Floyd Toole who hangs out there and I have the deepest admiration for, they are technicians pretending they know a thing about science when they don't.

Nelson Pass, Revel, Bose, JBL, Meyer Sound.  That's where t he actual scientists are.  I don't necessarily like the result of all of them, but their science and business practices are rock solid as a result.

I enjoy how Nelson tries different output transistors within his stash, in different circuits he comes up with in his head. Admittedly, 1 of 10 of those variations actually make it to production. He intentionally looks for rare or extinct opt transistor supplies to make it harder for people to clone his amps. Each variation and release sounding different from the past. Exploration never ends with him. Just gotta love it, rinse and repeat with new Opt's. All in search of a new and different variations of "sound" amplification.

I seriously doubt the majority of the self-proclaimed scientists over at the ASR forum have proper tools and platforms to measure all the various aspects of sound. Clearly many over there don’t use their ears much either, simply looking at graphs, charts, specs, produced by limited tools measuring only a few aspects of sound.

A fun read for those who appreciate the nature and physics of sound, so much more to it than a few metrics and specs used by techs too, have yet to see an audio lab covering much about sound https://physics.info/sound/