When it comes to isolation products it can get heated and expensive. I'd like to add something to the fray that's relatively inexpensive and thoroughly effective but it's too soon for me to say whether it's the right thing. It's because the effects are immediate and apparent but one must be patient and tune this product to their liking.
Les Davis Audio (from down under) has come up with a 50 mm wide, 1 mm thick CLD (constrained layer damping) product that you place under the footers of your gear. It can also be placed between monitor speakers and their stands. It's recommended that you try two discs under each foot and that sometimes only two treated feet are needed instead of all four.
The outer layers are aluminum and the inner layer is some kind of proprietary viscoelasitc material. Les got the idea from aircraft applications. I found that two discs have too much an effect for my tastes and I'm trying just one for awhile to see how it sounds over the long run. Anything I've tried in the past hasn't bettered the standard feet of the Marantz Reference gear I have (Ken Ishiwata knows his stuff).
The effect is like going from a very large room (before application) to a smaller room with just one disc to smaller room with two. The thing is it seems that you don't lose any detail or info. As the soundstage lessens, a kind of overcast develops. It's more of a hue than a tone thing, a kind of enriching. The lessening of the soundstage seems to be only front to back, leaving the width alone. Vocalist that stand before me at the edge of my ottoman retreat some, closer to the plane of the speakers. That's the best analogy I can think of for now. If you're dealing with microphonic problems (tubes, light weight gear, etc.) I can see where they can be of great benefit.
They sell for $100 AU (about $76-$88 US) and there's two dealers stateside that sell them for $125. I got mine for $99 plus shipping from amazon. They come 16 discs to a pack and it seems to be money well spent.
Next up I've got to see (hear) how they work under my monitors.
All the best,Nonoise