The wall outlet does raise impedance and restrict current flow, but it is just the tip of the iceberg, remember you still have an outlet and IEC connection after the Torus and they do raise impedance but it is necessary of course, and with quality connectors the increase in resistance is negligible. The real benefit of a large isolation transformer is eliminating the entire high impedance circuit going back all the way to the nearest low impedance current source, which is the step down transformer on the street.
That street transformer provides low impedance power at household voltage, but in travelling along 300 feet of aluminum wire to the meter, more aluminum wire to the service panel, through breakers and screw down buss terminations, then another umpteen feet of thin copper romex with twisted wire nut connections and brass duplex terminals in shared circuits - the impedance rises a lot at each mechanical contact and high resistance conductor thereby restricting current flow. The isolation transformer allows a reset to very low impedance once again through the magnetic reservoir of the transformer core. The wall outlet can provide sustained current enough to keep the reservoir filled, but not enough to for musical peaks.
The isolation transformer supplements power transformers in components which are often undersized by designers to reduce cost.
To me this aspect of power conditioning is far more important than noise isolation or filtering which is probably the reason why most people buy an isolation transformer, thinking of it more like a power filter. I use a large power conditioning transformer and the difference without it is night and day.
Rich
