I have used Herbies products and I think you need to decide if you want to couple the sub to the floor or isolate it. I use Townshend Podium products to isolate my speakers from the floor (suspended wood) rather than coupling. Isolation made a significant difference and for my application, they are a essential componet.
Vibration dampening
After reading the article on Herbies isolation products, I got to thinking: My sub has more vibration going on than anything else, at higher volume you could put your hand on top and it feels like a massager..I am using spikes on thin carpet with concrete underneath. Has anyone had positive results with these or other isolators? It is a Velodyne DD12.