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

If you 'must' have a particular amp, that most importantly affects your choice of speakers, i.e. amp's power will need ____ efficiency speaker, in your space, at your desired max volume. 

Even if what you 'must' have is powerful, I always recommend efficient speakers so you can eventually try tube amp(s) within an affordable power range where there is more options.

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Pick your efficient speakers first! Within the 'efficient' category, find speakers you 'must' have. After speaker selection, knowing your space and volume preferences, you know how powerful an amp you will need. Then find an amp you 'must' have within that power category.

Enough power? IF not too much = less: money, heat, weight = more placement options.

Minimalist, but not totally:

I must have remote volume, mute, and remote balance from my listening position.to refine individual tracks the engineer’s didn’t get perfect. Or the equipment/system isn't getting it perfectly. Balance, enjoy now, check everything in the morning.

A very small balance adjustment can make a large difference to imaging, not just the center i.e. singer, but more distinctive localization of backup singers, other musicians, giving a more involving experience.

Another advantage: If you learn to listen for, appreciate distinct instruments, imaging, then when it is OFF, it is not easy to ’let it go’.

R2R, you have individual volume settings L and R, watching meters is one thing, and who knows when matching signal strength l/r are correct using the beginning of a program’s content. delivered sound to your listening position is the real thing.

Oh, I missed the point, what would WE choose? What would I choose?. 

I thought you meant, you had already see an amp you 'must' have.

15k budget, that's more than I would spend, I have efficient speakers, so I have the advantage of staying in 25, 35-45 wpc range which are more affordable.

I researched, chose my Cayin, love it, it never occurs to me to consider another. That left me with 12K to spend on other stuff. Well, I would like external bias adjusters and meters.