[GeoffLee]

I could be wrong, but I would have thought that the mono button on the mbox2 has the same function as the mono button on the mbox1, ie so that you can hear live inputs thru both sides of headphones or monitors if the source is mic/line1 OR mic/line2. Otherwise it would annoyingly come from the left or the right. This assumes that the playback/input knob is set someway to the left. So stereo phase cancellations can be checked for at input source, but not the LR mix coming out of the main stereo outputs. This is different from the 002 (and presumably the 003) where the mono button combines the output signals to mono, so phase relationships in the stereo mix can be checked.