Well ...
So far in your post, I noticed you mentioned :
*mics
*tubes

*converters
and a brief mention of rooms.
Hell, you even mentioned mic stands, for cryin' out loud.
But I don't think I noticed even one mention about the source. Now I apologize in advance for making an example of your post, here -- so keep in mind this is just another one of my classic rants and it's nothing personal. But at times, I feel like there is a collective learning disability amongst the general amateur home recording enthusiasts.
Serious tweakheads like yourself, Bob, I imagine can literally spend hours (possibly even whole days) swapping out caps, chips, and transformers ... all the while playing hopeful delusions on your ears that they're going to somehow make a .00001% improvement in the sonic quality.

God love you guys for it, because some of this stuff does make a difference, I'll admit. And I thank you for it.
Now I'm speaking from a certain amount of experience with this. There was a time when I was recording music close to full time. And I've tried tirelessly to help people to understand this, but most of the time, it's like I'm talking to a wall. Take this for whatever it's worth ... the quality of the instruments, amplfiers ... right down to the
type of strings being used on a guitar for a particular session ... the type of heads used on a kit and expecially the kind of cymbals ...
These are what matter. Perhaps it's just difficult for some people to comprehend that the type of stick or beater used on a drum kit will have a far greater effect on the quality and fidelity of the recording than the type of converter used. It's a humbling thought, but I'm telling you now, it's probably true.
Now the mic stand thing is still kinda' iffy.

Okay, I'll give you that much. Worry about the kind of converter chip being used before you worry about the metal used on the mic / boom ... although even that one might be iffy (particularly if it's a very reflective type of metal used in the contruction of the boom stand).
I think where the problem lies is that
people separate recording quality and fidelity from quality of the sound source. As if it's somehow possible to have a great recording of a bad-sounding source or vice-versa. What I am proposing to some of you who still have this antiquated way of thinking is this: Has it ever occured to you that certain types of instruments or sources
record better? To such an extent, in fact, that if you were to compare two different sources, the better-sonding source will trick your brain in to believing a better microphone or a better recording medium (or even mic stand) must have been used to capture that sound.
One of the things you mentioned was high end. Alright, let's go with an hypothetical example for this. Suppose on one of the sessions, Mick Fleetwood insists on using some run-of-the-mill Sabien hi-hat, ride, and crash cymbals. Furthermore, let's suppose that Lindsay Buckingham decided he liked the sound of heavier-guage strings and lost his favorite guitar pick so he grabs a super thick one. Now, suppose they're both in bad moods (Maybe one guy's pissed at the other guy for sleeping with Stevie) ... so they both start hitting their strings and smacking their cymbals really hard and rough.
What kind of an effect do think these things are going to have on the high end smoothness and fidelity of the finished recording?
MULTITUDES. And ya wanna' know why? Because some mixing engineer is going to be pulling his hair out ... losing sleep due to ear fatigue, and probably making bad mixing decisions due to treble deafness and stress from trying to make the high end on final mix even passable so that guys like Bob's Mods can talk about how nice it all sounds decades later.
You would not be commenting on it, because it would sound like ass. And the majority of the home recording masses would be saying stuff like : "I'll bet they used really bad converters on that album."
The quality and fidelity of the high end on some of these records can certainly be improved / enhanced by a good mastering engineer -- I'll at least give you that much. I've heard it, in fact, myself. And they freakin' better, for the rates that some of them charge.

But if you really want to know what good, quality, smooth high end / treble boils down to ... it's in the quality and technique of the instruments producing the higher frequencies. This includes the drum cymbals, the accoustic guitar, and some of the other little percussive pieces and odds and ends. Similarly, the secret to good, tight bass is going to lie mostly in the quality and technique of the bass guitar (including the type of strings used) and kick drum ... and very largely due to the bass response of the rooms being tracked in.