I am selling my Turntable Top that goes with my Symposium Isis rack--it only goes with an Isis rack, as far as I know. It is 22X27, and incorporates internal air cell isolation in addition to constrained damping layers. It is level adjustable, divided into four quadrants, accessible from the bottom of the rack. It provides isolation and damping and is especially good for turntables without an integral suspension.
I bought it in May 2011. Since then, I purchased the Rockport table you see (not for sale!) and it has remained in place. There might be some scratches on the Turntable Top from siting the Rockport, but they will likely be covered by whatever you choose to put on it--I am not inclined to move the Rockport to investigate, at this time.
I am selling to downsize and because I doubt that the Rockport benefits from this as much as my previous turntable did, which did not have a suspension. I can tell you with that turntable, the results from the Turntable Top were exceptional--it stopped virtually all the footfall problems I was suffering from. Dynamics were also substantially improved. If you're not familiar with the TT Top, think of it as a Symposium Quantum designed to integrate into the Isis rack.
I have never seen this for sale on Audiogon; the price as a standalone is $2000. I would be willing to consider offers for the entire Isis rack, , which has 4 shelves (including the Turntable Top), three roller block modules, and an addtional base station to handle heavy loads (retail approximately $6150 as configured.)
Shipping will be based on actual cost. I estimate the TT Top weighs around 25 lbs.