Greg C,
yeah, you can hit Mute, and as I think about my approach, I see that I am sort of a wise guy so I would go for the more elegant way -- if the amp is muted and anybody touches Mute or Volume Up or Volume Down, the amp unmutes. I think that most people would hit the volume control if the zone were silent before thinking to change the input, so changing the input is a method less susceptible to accidental un-"muting."

Also, since I always look at this process from the point of view of a programmed remote that can do macros, it is more of a natural to go to an unused input.