Practically speaking, the room of course is the first and last variable. Most of us just aren't lucky enought to rent or buy a house/flat on the strength (or not) of its sound room alone. And even if we were, exactly how are you gonna test your sound-room to be before committing? You could do a few quick measurements but an empty room will measure differently than one filled with furnishings.
So realistically, if we have to make do or work with what we have, the first thing is the speakers. Not only are they still the most distorted, voiced and variable link in the chain, their being well matched to the room or not will be a bigger hurdle to overcome later (or present no realhurdle) if the room/speaker combo has been thought of and matched carefully.
With the speakers selected, amplifier power, damping factor and overall voicing become the next consideration so the speaker determines the amp.
That's how I'd look at it. And I'd add that a lot of speakers are too much for the room they're used in and thus inappropriate.
Especially smaller rooms can cause bass problems and it's here where an outboard sub with perhaps inbuilt parametric EQ to notch out the 2 or 3 worst room node spikes can really help a lot, never mind adjust the relative bass balance which could be too high on a passive full-range speaker.
In a lot of cases, a superior sat/sub setup really is the ticket, and if the frequency dividing happens in the low-level domain prior to the amp/s, even better.
When I still worked at Soliloquy and made a living selling speakers (to dealers), the best-sounding combo we had, in my opinion, was the 5.0 monitor with the S-10 sub. Outperformed everything else up to the big 6.5 which
could outperform the threesome but only in a sufficiently large room.
A small active speaker with the necessary amplification and compensation circuitry built in such as pro companies make (or Paradigm used to) can really be an incredibly compact, high-performance package with all the voicing flexiblity an end user needs. HiFi is funny in how it has ostracized tone controls, loudness controls, mono switches, active crossovers and such. It's taken away flexibility which, if we had it, would often call an end to the endless upgraditis which is nothing but patch work and shooting in the dark, hoping for the magic balance by way of a combination that, by sheer luck, happens to work in that room.
When we trash talk tone controls or analog compensation/EQ circuits, we don't point the same finger at the passive crossovers inside our speakers. Same thing tho. If you take 'em out of the speakers and make them active, you've minimized a major source of veiling and nonlinearities. It's not that the parts or circuits in outboard low-level mode are any better. It's that running "active" with dedicated amps and nothing between amp and voice coil eliminates problems endemic in the passive loudspeaker approach - which of course is the norm in HiFi.
That's why I think Zu and WLM and companies like them are on the right track. They go back into the pro sector and integrate bits and pieces of what's common MO there into home hifi. Whether it will catch on large-scale isn't at all clear. Prolly not. Hifi-ers love the freedom to mix and match wildly and inefficiently. It's part of the whole appeal of our disease...
Of course if we relocate, we have to start all over again. "Welcome", sez the retailer, "I've got just what you need, friend." And so it continues
