E-I transformer vs ring transformer applied to isolation transformer in audio
There is no significant difference between the isolation performance of the two types of transformer, when built with an inter-winding screen connected to earth. This prevents any common mode spikes on the mains supply capacitively coupling through to the secondary. 

The symmetrical construction and lack of airgaps in the magnetic path of a toroidal transformer mean it tends to have a lower stray external magnetic field than an EI construction. When properly (uniformly) wound and operated well below saturation, very much lower indeed. Another useful benefit is the form factor, it's often flatter than the EI construction, useful for a thin format power amplifier. 


  (Audio system desire good sinusoid power input)


Not really, you've obviously been reading too much advertising material for people pushing gold-plated mains fuses, and other ways to part people from as much money as possible.