Although it's sort of the shonky ( ) way out, I bought a ground loop isolator since I knew it would work. The one I bought seems to be pretty decent quality and only A$20.

Apart from the lack of whine I don't think I can really tell the difference. This is exactly what I bought here

I still might try the pseudo-balanced circuit I have, but if this is just as good why bother really. I figured the input was balanced from here and also the ETM I have. This doco describes the circuit to convert to a pseudo balanced signal.

We bought a stack of new test equipment just recently. I might hook it up with a signal generator and receiver and see what kind of frequency response the isolator has when I get a chance.