Use blu-tac between the speaker and the top of the stand and see how you get on with that, way cheaper than isolation bases. Alternatively use a set of sorbothane feet which are readily available and fairly cheap on Ebay, or even squash balls cut in half.
You could also put a granite/marble plinth (use a couple of suitably sized kitchen choping boards) and spike or 'squash ball' them to decouple the base of the stand from the floor.