If you're happy with what you have, that's awesome! If you want to take it to another level, add another sub (or 2 or 3). You'll get a lot more bang for your buck out of that than buying expensive cables. Not that they can't help, but whatever improvements (if any) you get from cables will be subtle, at least to most people. Adding more subwoofers, especially if you have four of them will be more than a subtle difference.
How good can it get, really? - my stereo sounds amazing!
I really love my stereo currently. I keep thinking I should be looking for the next piece to upgrade - phono stage, stereo subs, etc., but honestly not sure what to change or why I’d potentially spend more money to achieve a result that’s lesser or equal to my current sound quality. I sorta feel clueless as to how to proceed without screwing up what I have. I know it can get better but honestly I’m at a place when I just don’t know how it can. Hmmmmm.... not a bad problem I guess. Open to suggestions for sure. Thx.