What is the most overlooked consideration?

This is a fascinating diversity of viewpoints.  Many valid ideas and perspectives have been raised so far.  It strikes me, though, that the fundamental question posed by the OP has not really been hit in the bullseye.  Perhaps the answer is so obvious that it goes without saying for most of us:  The first and most important consideration to be addressed every time we are going to buy anything related to our systems should be to decide from whom to buy it.  Or to state this as a first principle:  Pick your dealer first.

Synergy, through the entire audio chain. This will also include treating the room and having your ears professionally cleaned and detailed. 

Dual mono at a minimum

@devinplombier wrote:

I’m actually of two minds. I believe the "external" route is actually easier to implement, gives better flexibility, and is likely to yield better sound quality.

Good to know some people feel this way about it. 

On the other hand, I think there is a certain elegance to a high-end system that consists of nothing more than two speakers, especially when those are pleasing to the eye.

Definitely. Save perhaps a single streamer/DAC/preamp sitting solitarily on a shelf, it makes for a simple, clean looking system. 

Dutch & Dutch, Burckhardt, KEF, a French company whose name I forget right now, and others have produced examples of the latter. If only Dutch & Dutch could manage to get out of its own way, the 8c could be the best system 98% of people will ever own. Instead it’s an unmanageable walled-garden mess, albeit a fantastic-sounding one.

Never heard the Dutch & Dutch 8c’s, but they are very well reviewed. Another Dutch-based manufacturer, Grimm Audio’s LS1c active speakers on the other hand I do know, and fed by their MU1 streamer are a great sounding package. Not cheap, but when you think of the dough that can be spend on a separates, passively configured setup that would seek to achieve a comparable-ish performance, one realizes the Grimm system will turn out to be the less costly option, and - depending on preferences - most likely better sounding at that. 

@aewarren wrote:

I have to wonder why so many contributors here are assuming that something as basic as room acoustics is being overlooked. Are they merely misunderstanding the question and confusing "overlooked" with "most important", two completely different things?

+1

I have to wonder why so many contributors here are assuming that something as basic as room acoustics is being overlooked. Are they merely misunderstanding the question and confusing "overlooked" with "most important", two completely different things?

Grounding is overlooked and powerful...

Vibrations control is overlook too but less so than  proper grounding...

Acoustics controls of the system /room is the most important factor by far...

 The most important lesson is that no factor can replace another factor or even compensate for its lacks... This is why all working dimensions parameters matter...

 A bad dac, or a non synergetical piece of gear, cannot be cured or compensated really  by any other mechanical,electrical or acoustical controls...

 But a  simple tweak can give something sometimes no easy to buy  gear  upgrade will do ... (Schumann generators for example)