Amp first approach to building a system, anyone ?

People who already own and enjoy those amps, are likely to have experience with, and understand, which family of speakers will sound best when powered by their amps.  They may change speaker brands, but they are unlikely to move to an entirely different style of speakers if they plan to continue using the same amps.

Right. One thing is certain for me - I will not choose any speakers that don’t sound good with tube electronics. Giving up tubes is almost like giving up analogue, and some would say even worse than giving up analogue.

Vintage class A Levinsons and Krells also have a cult following, Gryphons too, I think, including their preamps and phono stages.

Your references to equipment bought and kept are brands that do require quite a sum of monies to buy into. 

I feel confident in my suggesting these are not fledgling purchases. The buyer is experienced with different equipment and is now adding a new finesse to the End Sound they are looking at to be hearing. 

As a newcomer, Build a System reasonably cheap, this will suffice and be great for being educational. 

End Sound that is more desirable to End Sound being produced will be discovered, if the interest in Audio Equipment bites. 

Only then does the enthusiast become enthusiastic about creating and End Sound that is fitting into their Unique preferences. 

Exchanges of devices to replay recorded music will then make full sense. 

Big VAC tube amps are absolutely worthy of an "amp first" philosophy. Almost all my favorite/best listening experiences were heard with a VAC behind them. For me, a great amp is the most important component after speaker selection. And indeed, the biggest system investment is into my VAC amps. I like to listen loud and prefer the sound of tubes, so that makes it much harder and more expensive to satisfy on the amp front.

Selecting amp before speakers is a bit of putting the cart before the horse, but I can still almost see that, given a good enough amp. 

I'm pretty much amp first on the headphones front (electrostatics) too.