Good but difficult question to answer. Regardless of your system at any level you can upgrade and get a much better sounding one as long as you are drawn to higher sound quality. You stop when the incremental cost becomes too high.
So, perhaps a suggestion would be to go to some high end audio stores… even if it requires long drives. Or find some local audiogoners and see if their systems motivate you and in what direction.
one of the questions you have to ask is in what direction do you want to take your system… more drive and slam , musical and natural, sound spectacular.
So, what kind of music do you listen to and what kind of sound do you want?
What kind of investment level could you make and what is your venue like?
Also, it would be really helpful to see your system in its venue now. There is a place under your ID to put photos, this is really useful to help us understand your current system and environment. Often great improvements can occur with the equipment you already have.