I also have a Garrard 301 in a custom bamboo plinth and i found if you put anything under it that was squishy you would lose focus. the best solution I've got so far is a sturdy three legged stand with 165lb slab of granite on top then the table, sitting on 3 sharp steel cones. this keeps the focus but takes away 98% of the noise, bar hitting the whole assembly with hammer. I tried sorbathane, and vibro pods and various other inexpensive types of isolation and in the end took another members advice and tried just the steel cones and they seem to be the best over all. I would like to try some of the more expensive footers out there that incorporate a cone and some mild isolation or bearing point to see If they don't muddy up the focus but give a little more isolation.
I also came from a fully suspended isolated table (Oracle Delphi mk4) and it was hard to get it right buy once you do you wont look back.