@danager It is a little bit of a chicken and egg question, in absolute terms. In practical terms my experience has been that getting good room treatment early solves a lot of problems you try to ascribe to speakers, cables and electronics. They help you listen better and you are more satisfied with your choices in the long run.
The OP was asking about a flagship product to build around and I know of absolutely nothing on earth that helps you build a great system more than having a good sounding room.
You don't necessarily have to pick out 100% of your room treatment before you go looking for speakers, but placing bass traps of the appropriate parameters, diffusors between and behind the listener and some side and ceiling panels is going to get you a lot farther in your audio journey than anything I know.