If you will indulge me some of your time, I would like to know what tweaks have worked in your systems and which ones haven't. I suppose we should define "tweak." Somewhat arbitrarily, I propose, "Any addition or change to your components not recommended by the manufacturer." Now, you all can expand this definition (or narrow it) as you see fit. I'll start.
Tweaks that have worked consistently, with a variety of software: Argent "Acoustic Lens" (3 of them, one center rear and one on the outside edge of each stereo speaker), "Optrix" CD treatment, Synergistic Research AC power cords (the originals from 8-10 years back, $250 each), Cinepro Professional "Power 20" line conditioner (a line balancer, with 12 outlets -- 4 digital and 8 analog), Audio Quest "Lapis X3" interconnects, Audio Quest "Argent" speaker wire, bi-wiring my speakers, the screw-down clamp made by Basis for my Basis turntable (replacing a simple weight, also made by Basis), and the VPI record vacuum (the $500 model).
Tweaks that have worked some of the time: Bedini CD de-magnetizer, Aesthetix "Benz" MC cartridge Demagnetizer, various footers (some cones, some rubber or rubber-like).
Tweaks that have never worked: Room Tunes (corner or side-wall), coins on speakers, various more expensive wires and cables, different cabinets, SID CD Damping Mat (a green vinyl disc you put on top of your CD before loading it into the player), Shakti Stones (or any other rocks or weights designed to sit on top of components).
There. What say you all?