The OP asked why Naim don’t publish their specs.
I bought my first Naim equipment directly from Julian. Likewise the subsequent two or three upgrades.
Julian did quote and publish the power amp Watts and I think, their Volt.Amps into 8 ohm resistance. But he said this, THD and other such specs which were all the rage at that time, were pretty meaningless. I recall him telling me that “slew rates” and a few other things were more important. Best advice was to listen.
He wasn’t into mass market sales, so his personal guidance and that of his appointed retailers was probably more important than published “specs”.
I guess that philosophy lingers on despite a possible market expansion.
Cheers
Don