High end Class D amps?

Having owned the lot from Merrill to Nord to Rowland to every conceivable output board in multiple iterations, including Bruno's latest which to me sounded very similar to Ncore, tube input stages, transformer coupled input stages, etc etc..the best I achieved was with a Rogue Medusa with a ton of money thrown at it in part upgrades and it still could not quite match the best A/B amps and certainly not the best class A amps.  I concluded class D was very very good with attractive attributes when well implemented and for me best used as my summer amp or in an AV setup. I am still a fan but thought it to be limited.

Then out of curiosity this spring I grabbed an ARC DS225 from a few years back to use as a back-up in an office system backing up Valvet A4e monos at the time in the summer months. To my surprise, DS225 is easily the best class D amp I have owned and I would say on par with a top shelf A/B design of similar power. Not particularly sure why it should be other than perhaps a completely in house design by a company known for its tube products, ARC apparently spent 2 years designing its own output stage, a huge linear PS (which has also been a component of other class D designs I have owned and certainly all of the better ones). Where it differs from all others is having no global NFB and hence a more modest damping factor of 167. Sonically, its the first class D amp I have encountered that really suffers no dead zone, and is fully "on song" at the lowest of volumes. I would say its easily the most enjoyable amp I have ever owned listening to at low volumes, which I do a lot of at night. Bass which unlike most people I find typically to NOT be a strength of most class D because it is almost always over damped for the modern speaker, is stellar on the DS225, fast and articulate but with some body like bass actually sounds. The biggest difference though and where all others I have owned really fall short including the Rogue, it actually digs deep in the midrange to flesh out with some tone and grunge to acoustic and electric guitar for example, like good class A and even dare I say a good valve amp is know to do. My sense is the DS225 probably does not measure as "pristine" spec wise as say an off the shelf Ncore module, but that says more about the Ncore than anything. Grab one if you see one, somehow they fell through the audio crack into oblivion and no one really noticed. It happens. 

Atmashpere, how would one ever test that variable independently outside of other amplifier qualities? Plenty of seasoned audiophiles and reviewers alike that would argue subtleties in how a woofer is damped is second only to an amps ability to provide current into load variance in determining the best match.
I am listening right now to a pair of Harbeth 30.2 through the DS225 at DF of 167 at 8 ohm. I can swap in an Ncore amp I have on hand and the immediate complete unnatural over tightening of the lower register with a DF in the thousands has to at least be in part if not fully due to that difference.

Hey Ric, nice to see you around, 20 years ago I had one of your wonderful modded Dacs.

That was my point, how do you account for DF independently. My point too was more about lowish DF vs. the ridiculously high DF in most of the OEM modules, one of the keys to the bad sound of class D IMO, especially with my recent experience with the DS225. I get to this a matching issue, I listen mostly to easy to control 2 -ways.

I can say this with confidence, strap 20db of NFB on my DS225, gain match a test into a typical woofer with nothing but bass lines and I am going to be able to tell you when I am listening to to DF of 167 vs a significant multiple of that, and I would not need to hear the normal deterioration of the mids and highs. I would agree, amps sound different for a variety of reasons but extremely low output impedance class D amps share a house sound that to me is similar to way too much NFB in a class A/B design.