Atmasphere,
From your post near the bottom of page 1:
**As to sound pressure- we get about 90-95db of noise going on when mastering. The vacuum system is enclosed in its own chamber, but still makes noise when in operation.**
Unless that means something other than what it says, you're changing your story.
I understand your engineering principle, but I question the significance. Will a massive plinth transmit small main bearing movement to the arm base? Excite a tuning fork and touch it to a big rock and the vibration is turned to heat. Even if it does transmit it, the resultant arm movement will occur after the main bearing event.
What about micro movements you allude to? Not likely, and with the same time consideration.
Sound pressure waves hitting the platter are also hitting the plinth and arm at virtually the same time. To say that a plinth will insure coincidental movement between cartridge and record also doesn't make sense with regard to time. The impact on the record player is instantaneous and rotation of the record is continuous.
Regards,