I think he was referring to the generally much higher and more reactive impedance of MMs and the fact that these parameters may not be identical for each phase of the output in a SINGLE channel, using a balanced circuit. This creates a noise that cannot be cancelled by the balanced topology and is instead amplified. Channel balance has nothing to do with it. If I am full of baloney, perhaps Kirkus will correct me.
Actually Lewm, you got it exactly.
Now why do you think, do I have NO hum what so ever with a FULLY opened pre, going balanced into a balanced phono-line-pre?
Well I'd say that you happen to have good synergy between the cartridge, tonearm wiring, and preamp input stage, at least in the sense that its noise-rejection happens to be sufficient to completely eliminate interference from the particular amount of mains-frequency magnetic flux to which it is being subjected.
Now whether or not the ML engineers anticipated/designed for a similar level of performance in other situations or environments, I have no idea . . . but for yours, they got it right.
