I ordered a few 3/8" Sorbothane sheets from McMasterCarr.. Great stuff for isolation. I use it on my Zoethecus racks (between Z-slab and stand) and i recently plopped my Tannoy SGM10's on 4 2" pieces.
Great stuff!
http://www.mcmaster.com/#ultra-soft-polyurethane/=azvz5h