Class D is just Dandy!

I did try a pair of bel canto ref 500m monos a couple of years ago but for reasons I think mostly associated with the other gear I quickly moved on!

However in my ht rig the move to class d amp was a massive step forward in every way.
Replaced my Emotiva amps with a tiny single nuforce power amp making a claimed 150w x8, only using 7 channels for my 7.1 system.
The emotivas claimed 300w x2 and 250 x5, not quite sure where they were hiding those horses as the nuforce creamed them in every aspect.
dynamics, action, dialogue, sheer volume were vastly increased with the nuforce.
and now I have one tiny little box which has replaced two behemoth amps that were sucking juice and pumping heat.

I will at some stage give a pair of mono class d amps a whirl in my main rig again I am very sure!

Nearly forgot about my second system.
Linn Classik all in one which uses a 70wx2 class d amp and sounds pretty darn good for what it is and I have no desire to replace it with anything

There isn't time to read all of this thread, so my apologies if it's already covered the Red Dragon S500, but I've had that for almost two years and am really pleased with it.  Sound is detailed, balanced across the frequency range, bass is deep and articulated, mid-range is clear, treble is also clear and realistic though I sometimes think it might show a little more sparkle.   Certainly it's well ahead of the Class AB monos I had previously, and they'd been well recommended.  

The main partnering equipment is an Esoteric X05 SACD player, Townshend Allegri preamp, and B&W 804S speakers. 

I don't doubt that there may be better Class D power amps.  Some will be better because of their design and the quality of their components.   It's also possible that some Class D modules are better than others.   Living in Britain I don't get much opportunity to compare the sound of different systems.  I did hear one of the first NORD NC500 power amps (it's only an hour's drive to where they are made), but the demo wasn't very successful from my point of view - mainly to do with the circumstances and not necessarily a criticism of the amp itself.   Buying the Red Dragon was something of a risk because although I could return it within 45 days, I wouldn't get the import duty back and there's be expensive carriage costs.   But it's been highly successful and I'd probably have to pay a lot more to get something that performs significantly better; though in five years' time, perhaps, when things have moved on a lot, better quality may be available more cheaply.

I haven't seen much discussion of the NAD M22 outside of general discussion of the Hypex nCore modules, but I've had this amp for the better part of a year. It replaced an Ayre V-5xe which put out too much heat for the hot southern summers I have to endure. While perhaps it doesn't have quite as much depth as the Ayre, it has incredible bass definition and control, a wide soundstage, and a sense of liquidity, propulsion and flow that the Ayre definitely didn't have. It has a pristine clarity and neutrality without seeming anywhere near harsh, dry or boring, and the dynamics are thunderous. I really couldn't ask more from an amp. Considering I see the M22 going for roughly 55% off the MSRP around these parts, I don't think there's a better performance bargain for power amps on the used market.

I'm using a PS Audio HCA 2 with the Cullen mods and I love it. 

I auditioned a variety of amps in my home - a high powered ARC tube amp and a Pass Class A amp at the same time I had the PS Audio.  I think I may have liked the Pass amp about as much as the PS Audio, but I'm inclined to keep my gear turned on all the time I didn't think I'd like the extra heat and energy usage.

Time and innovation march forward so I'm sure there are others that are better, but I'm not feeling any urge to upgrade at this point.