Flagship product to build around

Speakers,

Amps

Pre-amp

DAC/Streamer also makes a big diffrence, however if you cant get the above 3 right the rest will not work out properly.

Suggestion would be to get a high efficent Speaker, High Impedance. This will work with almost any amplifier easily.

8 ohms at min but ideally 16 ohms would work a treat.

Soemthing above 96db,

The speakers/ room relation is to be build around not only with room treatment but some mechanical room control...(Helmholtz resonators and diffusers)

After that say bye! to most futures gear upgrades....

When music is there for the first time in your life, you forgot sound/gear upgrade...

Flagships products are too numerous at all price tag to be the center of focus... Pick one, chose well, and concentrate on the relation between acoustic/psycho-acoustic...

Or like most, ignore acoustic/psycho-acoustic and go for decades changing one piece of costly gear for another one and call that your taste...

😁😊

By the way there is no flagship "taste" in acoustic....Only a specific ear/brain tuning subjectivity at the command center of the acoustic journey and process....

OP asked for flagship product to build around:  

Luxman 509X.  65 lbs. of rakish Japanese amplification iron.  One can feed it anything of great quality for source and it will caress the signal passing it on completely intact.  

This integrated can well drive most any transducer on the planet.  And....it's gorgeous!  Audio crystal rarely matched, with its decidedly retro look, large room illuminating meters and solid Iowa-class battleship ruggedness.

My wife's system cobbled together until further refinement.  Presently fed by a Rega Apollo, Mojo Audio Mystique' 3 DAC and driving old Mordant-Short MS 20i Pearl Edition speaks.  Fun system, great lights, shiny.

MAGICO Q3s.

Start with your source. Drive your SETs directly; save money by eliminating the line stage. Since you'll probably never be able to site your speakers/listening position correctly like most audiophiles, room correction and equalization will be a big help.

Weiss DAC501