How do you know when a stereo sounds good?

"Do you have a suite of measurements that removes all shadow of a doubt that you are getting good sound, sound that you enjoy? "

In the spirit of audio as a hobby, you analyze the frequency response in your room. Being a gear head, kinda like having the dyno report of horsepower or the time slip from the quarter mile run.

Beyond that, IMO it's not about the music. Music is emotion. That can be stirred with a minimum level of performance with equipment from Best Buy in a bad room.

Base on some threads, some treat their system as if it's a musical instrument and they're the musician. Not my style.

When do you know your system is pleasing to listen to?

It's when the size of the sweet spot doubles and my S.O. curls up next to me, the corners of her eyes showing promise and mystery.

She turns to me and says, "I like this." And I'm not sure if she's talking about the music. Or something else. 

@dadork 

"It's important to me though to get it right with the equipment I have before I start thinking about upgrading anymore."

It is sad how many people in the hobby miss this point. Equipment flippers, take note.

Frank

because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know.

Is it clear now?

A stereo system sounds good when the experience of listening is about enjoying the music and not fretting about how the sound compares to some absolute audiophile standard. 

In my experience, listeners can achieve this by choosing their main system components and speakers to achieve the type of sound they most enjoy with the music they most enjoy listening to.  Cables and tweaks will not get you there if the main components and speakers are not aligned toward your preferences.  Once I figured out that tone and dynamics are most important to my listening enjoyment, then putting together a satisfying system became much easier.