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

I'll take the Gryphon Diablo 300.

The room we have, is the room we have for most people.  It can be treated in many was, but realistically, unless you are moving, most people are locked into their room.

If you choose your power amp first, you clearly are limiting your speaker choices, and vice versa.  I own Maggies, thus eliminating many amplifier choices and I am good with that.  My amps are McIntosh MC501s and the combination has pleased me for the last 15 years.

Good luck with your selections as building a system is a great joy.

The room we have, is the room we have for most people.

You are right...

I am lucky because i could acoustically transformed my room for my audio system... At no cost at all.... Esthetic dont matter in my audio room ....

But if your audio room is the living room, it is nearly impossible to install at low cost treatament and controls of the room that are cheap.... Esthetic means often costly... i imagine that it is possible anyway in a living room in some case of positive geometry, positive topology, and positive acoustical content materials...

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.