I think in this hobby, there are no absolutes. What I mean is, one type of isolation may better suit a certain component, while another will suit the other component.
For TTs, I believe the best is still a combination of high mass (granite or equivalent) and a medium density material (maple or composites). Granite by itself rings. Maple/composites absorb this ringing. Maple by itself does not remove very low frequency feedback from full range speakers. However if you put them together, maple/composite cancels out the ringing, while the granite removes the low freq vibration.
I would not recommend putting a TT high up between the speakers as this affects the imaging. Placing it low and/or along the side wall is a better option.
For TTs, I believe the best is still a combination of high mass (granite or equivalent) and a medium density material (maple or composites). Granite by itself rings. Maple/composites absorb this ringing. Maple by itself does not remove very low frequency feedback from full range speakers. However if you put them together, maple/composite cancels out the ringing, while the granite removes the low freq vibration.
I would not recommend putting a TT high up between the speakers as this affects the imaging. Placing it low and/or along the side wall is a better option.