obviously lots of caveats all noted above. But assuming you dont have some piece of junk along the signal path, and understand that big changes demand (proportionally) big spend, its almost always either:
1. Speakers
or
2. Setup
you can sometiems get a dramatic *change* from, say a powerful but cold solid state amp to a warm and flabby tube amp, but now you are in the realm of "i prefer this distortion to that distortion".
And i dont mean this badly, i KNOW what distortions i prefer. Consonant ones.
G