Once you hear the difference an IT makes, you realize: "Aha! So that’s what RC coupling sounds like!" And then you start hearing that coloration everywhere in mainstream audio equipment, and can never forget what it sounds like.
This is an experience no reviewer ever has, even if they have $250,000 systems. Because why would they? Everything has been handed to them on a platter. They don’t know what’s inside the pretty box... it could be elves doing magic tricks for all they know.
What drives this exploration is curiosity. What will this sound like? Well, you don’t know until you try, and why take somebody else’s word for it? That’s no fun.
Grounding in the physics of tube function helps, because you get a feel what the device "wants to do". Pilots have a saying, "the airplane wants to fly". If you’ve ever been at the controls of an airplane as it lifts off the runway, you feel it. The vibration stops, the wings lift, the ground falls away, and you keep moving forward, a creature of the air, not the ground. You are now in a different realm.
Tubes are the same. They want to amplify. It’s what they’re made for. Our job is to get out of the way and let them do that, so we get into load-lines, the most linear region, what happens as the current dips downward, staying away from trouble spots, etc.
I made a little post a few days ago on Facebook, quoting a meme from my Ukrainian friend, Misho Myronov. When asked what his amplifiers amplify, he replied: "Happiness! My amplifiers amplify happiness!"
All of us who create tube amps get this. We do it because it makes us, and our friends who listen to them, happy. In the comments to Misho’s post, I added:
"I was just talking to Karna, and said, an amplifier is like a dance partner for the speaker. If the partner is dull and disengaged, the speaker will be bored and not interested. If the dance partner is lively and fun, the speaker will light up and come alive."
All of us who have solved a difficult technical problem, or just got a better amplifier, will hear the speaker really come alive and surprise us. That’s the happiness.