Suspensions on turntable...really effective?

Dear Ct0517, To answer your question, I have two systems.  In both cases, the drivers are based on electro-static principle.  In one case, yes, the ESLs are driven by OTL amplifiers that do generate a lot of heat, but never enough to raise the room temperature by 10 degrees Fahrenheit (about 5.5 degrees C).  And no, I have never perceived that the heating of the room, such as does occur, has any effect whatever on the sound. (The other system is based on Beveridge speakers which are driven by Beveridge direct-drive amplifiers built into the base of each speaker.  Thus no audio step-up transformer in the signal path. Those amps use a solid-state input stage and tube outputs [4 per chassis] that have no measurable or perceptible effect on room temp at all.)

Geoff, if I isolate the turntable itself, do I need to isolate the subwoofer? 

It would be a good idea to isolate both the subwoofer and the turntable and all components really. The attenuation of passive iso systems is around 6 dB per octave. But you’re right, the subwoofer’s lowest frequency will be almost entirely attenuated by the turntable’s iso system, assuming a 3 or 4 Hz iso system that’s 99% effective by the time you get up to 20 Hz. The most aggregious frequencies for the turntable are circa 10-12 Hz since they would excite the natural frequencies of the tonearm and cartridge.