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?
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.
You may have already done this, but your speaker/listening position should be dialed in. Then start with room treatments. The best tools for this are an inexpensive laser level with a straight line and an RTA. The Behringer DSP8024 and DEQ2496 RTA/EQ's are very powerful tools. I do not connect mine "inline" as a cure. Depending on how experienced you are there may be a big learning curve. You'll know where your room problems are and be able to see as well as hear the results of your acoustic treatments. Most of us are dealt a less than perfect room, with these tools you can maximize what you have to work with. Also, you may not be able to detect the impact of many tweaks until your room/setup is maximized.
Walker SST silver paste contact enhancer is impressive, particularly on tube pins. But first, just cleaning all electrical contacts end-to-end about every six months can make a startling improvement.
What is your source? : turntable? cd player?