Regarding REL subs what they say for their , or any down firing sub, makes sense. But not for other subs perhaps? Re Harbeth, there are two approaches to vibration / energy make something heavy so it doesn't vibrate, make it light so it does. Harbeth use the later approach.
Rel Does Not Recomment Isolation Stands
This came as a surprise. I had just assumed that it should be isolated. Then I discover I was wrong. after doing some research for isolation for mine. Even though I am NOT electronics engineer I think this is an interesting subjet idea. Pardon my utter ignorance. I should have known there was an opposing view. Always is. Just didn't think of it