Well, I see a lot of different tweaks here, and will try some new ones. I think my favorite substantial one was to add these lead-shot filled "pillows" to the top of my speakers and most components. My system is in the baement on a concrete floor, so I have had no noticeable change with spikes on speakers, or on anything for that matter. I also had no noticeable improvement with innertubes, and the bubble wrap underneath components. But adding this weight to most everything changed my resolution to much finer. It was like clamping the speakers in a vice. Even though the cabinets were very solid, you could feel the speaker cabinets resonate. Now there is no resonance to be felt. The pillows are quite heavy. I initially thought it would cost around $20-$30, but ended up at around $100, because I also had to pay a girl to sew these things up too. But, I feel without them now it would sound "tinny" in comparison.
As a side note I have never been able to discern any difference using the RF blockers.
As a side note I have never been able to discern any difference using the RF blockers.