Hey Myles,
Regupol is the product you need, the thicker version (15mm)
Its a German product made from recycled car tyres, and is designed for machinery to stop vibration.
but you only need 4 small square pads for each unit, to do the job properly (think car suspension).
If you use a mat - then transfer of vibration will happen.
Happy to chat over the phone about how to do it properly (once)
You can purchase 1 square meter, and cut up 100mm square blocks.
Also very handy to have extra squares of it around the studio - for under monitors, bass amps, drum risers, isolating walls etc.
A great product that has served me well for years - for many isolation tasks.
http://www.regupol.com.au/brands/regupol/Check the pic on the website "rubber fibres with a low density" - that is the correct one