The discussion as to "what sounds natural" vs "artificial, over-hyped" is one that interests me. You always see audiophiles - and reviewers - talking about some approach to speaker making being more honorable, and for those who really appreciate "natural sound" vs "hi fi."
And yet you see audiophiles making that same claim, yet preferring speakers that are all over the map. One audiophile's "more natural/realistic" sounding speaker is another audiophile's "artificial" sounding speaker. The problem, it seems to me, is that we are currently stuck in the classic "blind men and the elephant" problem. Currently no audio system can produce thoroughly realistic sound (and add to that the limitations/colorations in the recording chain). And so the perception of what sounds "natural" or "real" tends to fall to whatever an individual focuses upon most as missing from, or included in, a presentation.
One person may insist on greater dynamics as being the barometer of a more natural system; another on smooth instrumental timbre, another on detail, another on fullness of tone, another on incisiveness, another on a relaxed presentation, etc. I can't tell you how many systems I've sat in front of were the owner waxed about how he preferred the less hyped natural sound from his components...that left me completely feeling the opposite. And so it goes...
I myself have favored using tube amps for many years - in particular designs that add a bit of classic tube richness - because one of the things that immediately strikes me as different between live and reproduced acoustic sounds is the relaxed and rich nature of live sound.
Tubes, for me, tend to help add just that quality - even if it's an artificial add on, the result to my ears is more consonant with live sound.
But that's simply what MY mind has tended to focus on. If you focus your mind on other aspects of live sound, you'll find them missing in many audio systems and want to emphasize that aspect (dynamics, clarity, pitch control, whatever).
One of the biggest boogey-man, as we've seen mentioned here, is the appeal to a rising treble, or treble peak, as being unnatural. However, in a sense I can see this as just one of the blind men speaking his opinion, while appealing to the part of sonic reproduction he finds natural.
I myself generally go for a coherent sound, so that high frequencies don't stick out and sit "in" to the rest of the spectrum in an unobtrusive manner. Yet I've heard many speakers that do just this...and yet sound "unrealistic" in another aspect: they lack the jump, surprisingness, "thereness" in many instruments.
I recently listened to a pair of speakers that were designed, in the end, to the ear of the designers who appreciate the vividness of live instruments. The speakers had a more prominent treble region, and something of a leanness overall. BUT....damn did they sound more "real" in many instances than even my far more expensive and neutral-measuring Thiels speakers. Percussion, drum snares, bongos, bells, triangles, etc had a they-are-there pierce the air quality that you can get from those instruments in real life. Many neutral sounding speakers can render a recording with a holistic fabric, but high frequency sounds don't "pop out" of the mix the way high frequency or percussive instruments can in real life. There WAS something more life-like about aspects of the sound, vs many more neutral speakers, and if that's what one focuses on, those speakers could be the "more natural sounding" type of speaker. That is one reason why a hyped treble has often been created in the first place - it can create a sensation that some find mimics a more "realistically clear and present" sound.