Thanks atmasphere,
I can't argue with what you're saying about the speaker sensitivity vs amps

Unfortunately I cannot change gain of the poweramp. Or, can I? I can change the bias current from low to medium and high, which sets the amount of Class A power, according to Gryphon. But that doesn't affect level of hiss.
It's just that I've never heard this amount of hiss from such high-end equipment before. Some hiss from a tweeter with your ear right next to the tweeter, yes, but at 1m and even from the midrange, I don't expect.
Moreover, other pre and poweramps I've tried, give the same hiss.
Note that it’s also the same for left and right and independent of volume setting.
I then wonder what one refers to when manufacturers or reviewers say that an amp has an extremely low noise floor, black backgrounds, dark space etc. I'd expect that means very little to no hiss at all.
Yet, I am starting to (have to

) believe what you're saying.
Cheers