How do I know if my systems any good?

Take time with what you have; not only your gear but your ears. Move your speakers around. Look into placement theories. I found the Vandersteen method worked for me. Make sure you can get everything out of what you have before you make a change. 

Welcome back @mahgister .

All of what you said is right...

But your forgot to mention that nevermind our different tastes, nevermind our different histories,  we can all understood what is a good soundfield when we meet and immerse in it, as you rightfulle said BUT  you forgot to mention that there is a reason why? but you guess it right... There is an objective reason... Acoustic is the reason why... And acoustic has nothing vto do with taste...

The same reason by which audio science progress, not only in engineering is  acoustic and psych-acoustic experiments ...As the revolutionary Choueri BACCH filters for example or the tuned resonators grid in my headphone...

All audiophile vocabulary express something about audio component experience which is subjective.... But acoustic science is objective facts and psycho-acoustic too and help to understand our experience and putting concept on it.Then help us to design simple listening experiments to improve what we already own BEFORE blindly upgrading it...

Elementary very simple basic principle in acoustic guided me toward sonic heaven  with listening experiments... Most audiophile ignore and dont bother themselves by experimenting with it and this is the main reason behind consumerism upgraditis and frustration,...Nothing else...

@mahgister: Well, assuming that the sound perception is personal and subjective:

What would be the point of discussing sound systems and good sound in general if everyone has different opinion and sound preference. And how do we explain the fact that most of us agreed when it comes to good recordings, good music venues around the world, good symphony or musical performances in general, good hi-fi shows or bad ones? Obviously, we hear and perceive sound in a similar and uniformed way. On the other hand, I agree that we have different preference in music genres and that might well influence the overall expectation of one"s sound system performance. However, that should not be a major factor when it comes to a good objective sound perception of music. 

Thanks for your kindness my friend...

Welcome back @mahgister .