No, that's not the issue.
The issue is too much dissipation at idle for all but the Purifi and the new NCX modules. I've tested enough of them to know an NC500 with an appropriate SMPS will be disipating over 20W at idle. Put two in a box and you have 40W.
You might say 40W is nothing. But you'd be wrong. 40W in a unventilated or poorly ventilated box means internal temperatures rise well into the failure mode area. I've just had yet another Hypex based class D stereo NC500 amp on my bench (an early NORD one). It had cooked itself (44W measured at idle), as had the unheatsinked Sparkos 'discrete' regulators and the 'discrete' opamps by Sonic Imagery. All in the trash where they belong. They pull enough current on their own to run hot enough to die. That said, even when running from the onboard SMPS linear regulators and a sensible OPAMP installed, the internal temps are still too high. I've advised the owner to put twin variable speed computer fans on top of the amplifier and not install it in a rack.
The two SMPS transformers on each PSU have components sitting around 85 degrees Celsius when idling and playing nothing- just turned on. The output filters on the NC500s are up to 95 degrees Celsius! That's 203 degrees F. Now you don't need to be Einstein to realize what happens to components sitting up against that sort of heat for the long term. They die.
The heat producing transformers and OPT filters have no ability to get rid of heat effectively. They can't be heatsinked easily. They need forced air cooling. This Nord had ventilation slots in the base, but they were mostly covered by the installation of the SMPS supplies and the only space for air to enter was a 2"x3" uncovered vent space. The entire cabinet is aluminium and the top lid ventilated perforations, but that doesn't matter. Spot temps on particular components are too high.
The other amplifier was also a Class D which pulls 30+ watts at idle with NO ventilation whatsoever. Completely sealed.
The third thing on my bench last week was another heat related issue. But it was a DAC from Benchmark. Again, completely sealed cabinet, pulls 10.2 Watts in operation and gets too hot inside that tiny box. All things from the Northern Hemisphere where it is cold more than it is hot. No good down under and we're not even in summer.
If I wanted a Class D, I'd buy a Purifi implementation from Boxem. His cabinets are ventilated, mounted properly and the modules he uses have the lowest idle losses.