I would put room acoustics as #1, speakers #2, followed VERY closely by subwoofers #3, sound processing a distant #4 and lastly amplification #5. You are comparing professional sound recording to consumer playback. Two completely different worlds. I'm guessing the DACs available to the professional studios are not found in most if not all of our consumer electronics. The DACs in modern AVRs, pre-pros and what not are all very close in quality to each other. You would have to have perfected #1 and #2 before you would be able to measure a difference let alone hear one. Professional studios are built with this in mind I'm guessing. Not so with living rooms, garages, dens, bedrooms, etc that double as our entertainment rooms. What I'm trying to get at (in my opinion) is that you can't take a professional sound engineer's criteria and apply it to your own scenario in this case.
Here's my anecdotal experience: I have a fairly decent setup which consists of Revel Performa2 F52 speakers, Denon AVR-4311 receiver, Oppo BDP-95 for the source, and an Emotiva XPR-5 for amplification. Unless I'm listening at over 90dBs (sub not included), I hear absolutely no difference when the speakers are driven by my receiver or the external amp. My room is very simple, sealed and well treated for first reflection points. I always get that warm fuzzy feeling of near nirvana when listening to music on my system. I took my entire system over to my parents' place. Even after spending the better part of a week trying to set it up it still sounded mediocre. His living room is an acoustic nightmare with high ceilings, hardwood floors, multiple glasstop tables, windows everywhere, large sections of effectively bare walls, leather seating and a huge entertainment center that forces the speakers to be stuck in corners. The speakers barely sounded better than his existing $200 a pair Infinity P363s. These same speakers sound amazing in my room BTW.
Fortunately, after getting tired of mediocre sound he has given me permission to put up temporary room treatments to prove to him that spending $$$$ on new speakers is not the way to go in his case. I advised that a few hundred in room treatments will make a huge difference as opposed to thousands on new speakers on marginal improvement. Well, that's my $0.02 and personal experience on the subject. Sorry for the long winded post.