How about placing the one rack with the turntable in the sand...?
The general idea is to get your vibration control as close to the component as possible. Easy enough to experiment and determine for yourself. What you will find is putting a rack on a sand box and then putting the component on the rack is nowhere near as good as putting the rack on the floor and the sand box under the component. Turntable, CD, whatever, same deal.
The biggest misconception, and its a real common one, is that its all about isolation. This one you can disprove so easy it will make your head spin. Simply have someone go pick up your CD player or whatever while you listen. Minute they pick it up its isolated. Does it sound any better? Not on your life. Because its about vibration control. Even a turntable, most of the vibration that needs controlling is generated within the device itself. You could float the thing in orbit, couldn't get more isolated than that, still gonna need vibration control.