How do you know when a stereo sounds good?

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.

When I get goosebumps or chills I know its good. However, the real test is certain songs will bring me to tears. 

hilde45   + 100

A wise and reasoned response.

Questions are bizarro

This is a question that gets me in trouble all the time; maybe in a different way than you are asking. I have had my system set to where it sounded really, really good; better than anything I have ever heard. I am sure from reading this forum that it  isn't the greatest out there but for me and my limited experience it's damn good. But then your question comes to mind and I start tinkering with speaker placement, crossover setting and such thinking it could be better. Unfortunately I usually lose the magic and have to start all over. It's important to me though to get it right with the equipment I have before I start thinking about upgrading anymore.