How do you know when a stereo sounds good?

There is no right or wrong in this hobby. There are only personal subjective preferences to what makes music sound good to each individual. I don't understand why that is so hard to understand and accept. 

Because while there are rights and wrongs, or at least valid and false claims. That is what is hard for many to accept. It's fun to believe in magic, but magic is illusion. It is not real.

There is not right or wrong in people attitudes...They are free and had the right to their own experience and justification...

But in audio there is right or wrong about   to manage the way to reach a good S.Q.

For example basic acoustic installation active and passive is way more important than the choice between 2 good pieces of gear for an upgrade....

How do you know your gear qualitative peak without putting them in an optimal environment?

Who want to upgrade "blindly" or partially deaf because he does not know what his speakers/amplifier/dac are able to do in an ideal room, who want upgrading based on publicity and without any control on mechanical, electrical and acoustical working dimensions?

hilde45

I think the purposes of the OP’s questions were to see if anybody had an explanation different from "I just feel it and know it." I agree with you that the vast majority of the answers will likely be that one, but that doesn’t mean someone might have a different way of saying it or a different perspective. To you, there’s only one answer and the question was meaningless, but you can’t know ahead of time what the other answers will be. Maybe someone will surprise you with an answer you hadn’t yet considered.

And you still didn't explain the science fiction part of your reply.

First, someone who sell pieces of gear will say: your feeling about yourt system is not enough... You need this piece of gear to increase your experience...The measuruments AND your listening experience would say so...

Second, it is not false to speak like that, but ANY "TWEAKS" must be experimented in a good acoustic settings first... WHY ?

Because many costly tweaks even good one COULD be useless or way less useful in a good acoustic settings...

I sell creativity not products...

Acoustic is the black matter in audio and the elephant in the room....NO TWEAKS in my system could replace my acoustic treatment and controls anyway... Even those i tried and which  worked well... NONE....

Your room acoustic treatments are tweaks. You are modifying the spatial volume of your room or affecting how the sound waves reflect or diffract. Whether you modify signal before the speaker or modify the sound waves after the speaker doesn’t matter. You are still tweaking the sound to suit your own personal belief of the ideal sound. Your ideal of what is good is not necessarily anyone else’s ideal. 
 

If you have to tell people they are believing in magic because you can’t hear what we do, then you need more art in your life.