After moving house a couple of years ago, I'm now in an (overall better sounding) upstairs room with hardwood floors and a good, solid sub-floor. I came from the basement with 6" fiberglass reinforced concrete floors (which offered excellent low frequency resolution and power).
I'm still working on a suitable footer for my speakers as the suspended floor tends to sink a lot of LF energy. The Herbie's decoupling gliders were absolutely awful for me (YMMV). Yes, they got rid of some vibrations, but they also left me with a tall 200+ lb speaker that wobbled worryingly, and a sound that could only be described as dead and uninvolving, like someone threw a heavy quilt over both speakers...Herbie makes some good products, but these just didn't work in my application. Currently, I'm back to the stock brass spikes on brass discs. There are other so-called 'decoupling' contenders, but none of them come cheap: The Wave Kinetics 2NS (around $1600 for the set) and the Track Audio spike kits (around $1250). I would welcome thoughts on either design.