Posted 22 January 2014 - 04:17 PM
I never followed up with you all. Sorry, life got really busy. Hopefully nobody else will have the same problem, but just in case. My m20 was in fact defective. The mute all button did not work. It lit up when pressed (a slow pulsing light) but nothing was muted. It was replaced at no charge and the new one works great. FYI, when you press the button, you hear a distinct relay click, and all outputs are silenced. The broken one did not do that.
Anyway, all's well that ends well.