I think that room treatments generally, of which bass traps are just one element, to be the most significant thing you can do to your system. I hesitate to call them "tweaks" though. I think of room acoustics are an essential component of your system.
Tweaks with overpowering resuults.
I checked out the posts on tweaks and found lots of suggestions, but didn't really seem to find a thread that listed tweaks that were overpowering. You know, the result wasn't subtle but in your face. I admit that I have ears of tin and tweaks go right passed me. So far, one of the few things I tried that really astonished me were the diy bass traps that I put in the corner. And this is probably because before they were there, I had this nasty boom going on that has sense disappeared. You might say this tweak had the effect of removing something I heard as opposed to hearing something new.
Any more?
Any more?