"IIRC, the dimmer input doesn't have a pull up/pull down on it at all, whereas the cellphone mute line does have pulldown on the mk2a. If you have no pulldown then you're unlikely to affect the workings of the signal line - you will just snoop. A diode won't help here."

Hugo,
Does this mean if I am "snooping" with the mute line it is safer to use an MK2 not an MK2a?