I see what you are referring too now by pseudo-balanced.
I have actually already tried lifting the earth so that you have bal hot -> unbal signal and bal cold -> unbal ground but that didn't work.
I think, as you identified, the balancing on my outputs is not achieved by transformers and is perhaps not ideal.
I will try something like the cleanbox but it has got me wondering that if there is already hum being introduced into the signal from just the hot and cold outputs this must have entered the signal some way upstream and simply transformer-coupling this signal to the inputs will still transmit the same noise. I hope not.
Anyway, thanks for the help - I'll let you know.