Can I ask why not? I have done as you suggested, but I think they are tied together at this point in the Prefix. Presumably it is because it will effectively be one long cable connected to earth by a cap as opposed to two discreet cables that are each connected to earth via a cap?
Earth loop.
They are tied to earth at the board, so must be kept isolated everywhere else.
What was the solution, bigger cap on input, or fiddling with earth on deck/arm?
Well the Aro pivot is also decoupled electrically as the cup is Sapphire - but the arm-tube is independently earth wired through the multi connector.
I think I will just have to buy some styrene 2n2 and 1n5 and try them.