Isolation platforms for turntables

I agree that you should not have all that gear between the speakers if possible. A lot of times it's not possible though and you have to work with what you've got. It's quite amazing how much difference you can hear though when you move your racks out from between your speakers.

As far as isolation of the turntable. Pretty hard to beat the vibraplane.

12-19-13: Onhwy61
I suspect your loudspeakers effect your turntable more via airborne sound waves than any structure coupled vibration.

12-19-13: Elizabeth
The other way would be more mass in the TT stand.

I'm certainly no expert, but I agree with the 2 above statements. I think what makes most sense is to try to get those airborne vibrations out of the TT. So the TT coupled to a heavy base is what I would do. Actually what I plan to do over the Holidays with my table (Spikes on my TT and sitting on a sandbox I have yet to make).
That, as opposed to damping / something soft under the TT. If you do that, the airborne vibrations have no place to go.
I also recently moved my rack back closer to the wall and it seemed to help.

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I think if you can move the turntable to the centre of the rack and floats the rack with some kind of support/feet then it should be fine. Adding Symposium will improve better. You can move your speakers a feet or two out form the front wall.