Hi Sid,
I've heard all kinds of devices that go under shelves and different types of shelves. Most of them are subtle differences. I was totally blown away by what I heard, when I put my VPI Aries on a Neuance shelf.
I do have a butcher block sitting between my rack and Neuance shelf. The reason I did that, was that I preferred to level the table by putting stuff under the maple butcher block instead of adjusting the legs on the Aries.
Here's a fairly recent picture, before I added my SDS.
http://members.aol.com/bvirgil311/Rack2.jpg
Have a great day,
Brad