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

This is not how it usually happens, but what if you simply must have a particular amp and then move with upgrades in both directions? Let's assume that the only source will be RTR deck, so no preamp will be needed.
The price about $15k new or used ?
This is a hypothetical exercise, I am personally not prepared for that yet. However, it would be, theoretically, perfect minimalist audiophile set-up. 
I myself would probably choose either Lamm monoblocks or Gryphon stereo power amp, both used of course.
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.   
If my room changed and it required changing speakers, I’d probably change amps to match my new speakers.