What was your first tweak?

The flat discs that were held on to the top of the cd with adhesive was probably my first tweek. They did improve clarity in the treble. Next came the reference bands that stretched on to the outer edge. They were good too, easier to use, and removeable. I would still be using them, but I got a Pioneer PD-S95 transport that clamps the disc, and makes their use redundant.

Headphones. None will bother me cuz I hear nothing.

Way back in the dark ages, I read that tonearm damping was the coming thing in consumer audio. We just called it hi-fi. Must have been in the early 60s. I had an Empire turntable and arm, and the article I read said to get a paper clip, bend one end tightly around the arm -- more or less at the arm'smidpoint -- and set up a dish of some kind (I used the top of a Shure cartridge box, upside down), and fill it with STP. Then stick something on the bottom of the paper clip that acted as a little paddle when the contraption was lowered into the STP goo.

Well, darned if it didn't work, or at least I thought it did. Amused my friends, too.

Way back when (around 1990) I sent my Philips CD-80 to Stan Warren and had him mod it for me.
It worked. The sound was more open, detailed and dynamic.