Building new system starting with power amp. What would you choose ?

stibi, I agree with you, I would consider Lamm first. Question is which one.
Diablo 300 is a very fine choice if you want transistor amp, and it can easily be found used, there are couple here right now. 

What if someone special gave you your favorite amp as a gift ? You would want to start building the new system from this, right ?
Another thought. Many speakers are actually better than they might seem but they do not perform their best because the amplification is not good enough.
Lamm, Gryphon, Nagra, D'Agostino would work very well with a wide range of speakers. Not sure about Levinson ML-2, besides try to find it, I guess.

The room you have; might not be suitable for the speakers you're considering.  The room might very well be the reason to reconsider a specific speaker for one that will work within it.

That might be another reason to start with the amp. Room might change, speakers might have to be replaced, but your favorite amp will stay.
In my case, I will never have very big room and I listen at moderate levels.

Purifi by VTV at <$1500 or spend a little more and get the NAD  version, giant killers

The only amp I “simply must have” is the one that works best with the speakers I love.  My audio DNA just don’t work the other way ‘round.  A couple that might get me thinking a little though would be the Valvet A4e mono blocks or maybe a Raven tube amp.