How do you know when a stereo sounds good?

How do you determine that you enjoy listening to music through your stereo? 

I guess I'm not sure what you're asking. Taken literally, this seems to be asking for another perspective besides my own internal voice. It's like asking the question, "Am I in pain?" That's not a question I can make sense of without some kind of science fiction scenario.

If your question is, rather, "What can I do to experiment with my stereo to see if my experience changes for the better?" then there is a wealth of literature available, including many free videos on youtube, etc. 

When Listening to music becomes an “event”, where I experience the music and become emotionally involved.  When the music moves me and my setup pays for itself with each song played..  When there is almost nothing else I would rather be doing.. When my systems disappears and only the music is left.. 

When I’m not looking on here for new gear… 

I know it sounds good when the music coming out of the speakers matches what I think it ought to sound like.

When I play a recording I've heard a million times and hear something new I never noticed before.