WOW factor

Just wondering what upgrades or changes to the system made big differences in sound in your system?
For me there were a number of things, but I'll start with: suspending my speakers from the ceiling using cables attached to rubber mats coupled to top and bottom of speakers held in place with cables. Prior to that I had plywood squares coupled to speaker's top and bottom surface which produced alot of bass resonance. The rubber mats made the sound dark and quiet. Also floor does not resonate. This is one of many things I discovered.