The even order distortion cancellation that Soundhound mentions is a characteristic of the balanced stage itself. In other words, it cancels the even order distortion products that the stage would otherwise produce itself were it not a balanced design. All circuits produce some distortion products and it is the ratio of even to odd harmonics that he is concerned with. With many off the even order (euphonic) harmonics cancelled, the more harsh and offensive odd order harmonics are unmasked and become the dominant sonic characteristic of the amplifier. This is a separate issue from the noise rejection abilities of the balanced input circuit.

Apologies to Soundhound if I have mischaracterized his opinion, which he is more than capable of defending himself.