TT on Symposium Super Segue - slate or maple underneath?

@tonyptony: What you want is stiffness and non-resonance. An easy way to reduce resonance is to install constrained-layer damping (Green Glue, ASC Wall Damp, EAR IsoDamp) between two stiff (and possibly dissimilar; your 3" maple block and 1/2" piece of slate qualify) materials. You want stiffness for a couple of reasons; a particularly important one for a turntable is that the greater the stiffness of a platform (all else being equal), the higher it's resonant frequency. You want the support structure's resonance to be as far from (in this case above) the turntable suspension's resonant frequency (and that of the arm/cartridge) as possible. 

Geoff Kait recently here on Agon (in the thread entitled "Component vibration isolation question") provided a link to the tutorial on isolation by Shannon Dickson in a 1995 issue of Stereophile. Do yourself a huge favour and read it. In it you may find the answers to many if not all of your questions.