After I had my dedicated lines installed I got a Topaz Isolation transformer. It did drop the noise floor a bit. I have since removed it because even though it is 1:1 there was a 2V gain on the output and my voltage at home varies from 119 to 127. That makes me nervous running my tubes from there. Remember it just isolates not regulate.
As far as the earth ground - ground the input as if it were normal. The output if balanced it will have the ground center tapped on the output of the transformer. That greatly reduces common mode noise. What you will read is is 60V between hot and ground and 60V between neutral and ground. It will read 120V between hot and neutral.
As far as the earth ground - ground the input as if it were normal. The output if balanced it will have the ground center tapped on the output of the transformer. That greatly reduces common mode noise. What you will read is is 60V between hot and ground and 60V between neutral and ground. It will read 120V between hot and neutral.