We've exactly the same system on UK 240V. Neutral is grounded (ie connected physically to the soil) at the electricity substation, and at regular intervals underground. Only two wires come out of the ground to the electricity meter (live and neutral), with the domestic ground wire attached to neutral at that point. Since the neutral wire inside the house takes the return current, it floats an unspecified and usually horribly distorted ac voltage above house ground as a result of wiring resistance and ac impedance.
I've been thinking about a balanced isolation transformer for the audio system for some time, so interesting to see that you have gone a similar route.
Craig