CK,
Watts/power alone is solely about how loud it can/should go and not useful to determine much else.
Other characteristics of amps and how they interact with speakers, like damping, current delivery, transient response, and other aspects design and execution have more to do with control, musicality transients and such. Specs in these areas might help set relative expectations but do not tell the whole story either. Only your ears when listening can.
Often the build quality of the power supply and transformers are good indicators of what might be expected.
Class D switching amps are considerably more efficient in delivering power than Class A or A/B. As a result, the power supply circuitry is considerable smaller, lighter, and compact. Also less heat is created in teh process so heat sinks are smaller, etc.
My understanding though is quality of the power supply is still a major factor in resulting Class D performance and power supply quality varies widely from model to model, vendor to vendor, despite the more compact package.
So just like most other gear, not all Class D amps, even all Icepower module based Class D amps, are created equal.
Same true in regards to Icepower amp input circuitry and how designed to work well or not with higher output impedance tube pre-amps. There are differences from model to model, vendor to vendor. Wyred is quite good in this regard as I understand it.