What is the most overlooked consideration?

@phusis 

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.

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.

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.

It's the room. It has a greater influence on what you hear than any source, amplifier, speaker, or processor. And if you argue it doesn't apply because you don't plug it in, realize the end result is akin to a DSP, only better.

IMO Serviceability. Can it be repaired if needed? Either by a company or technician that specializes in that particular product, or by relatively easy access to the factory, preferably in my own county. Also certain gear in today’s world cannot be repaired, but needs to be replaced, so that’s a consideration as well. 

@aewarren 100%

Is this fun?  If buying a piece of gear (new or used) from shopping to buying to opening the box to setting it up to listening to it isn’t fun for you, something is amiss.

Also, will the new piece of gear allow you to enjoy listening to “Exile on Main St.” all the way through from Rocks Off to Soul Survivor.

YMMV

kn

Quality stands for equipment and speakers.  What components and speakers are placed on dramatically influences everything from noise floor to sound stage and dynamics.  Few years ago I placed a very respectable system initially on an IKEA bench, (yes I know better), then finally placed everything on a proper Quadrasprie SVT stand, beyond shocking.  I knew better, but wow!  Everything radically fell into place.

Many items outside components and speakers are overlooked, I find that particular item the most frequently dismissed, misunderstood and oft poorly executed.