Originally Posted by Eric Pederson
With software you'd have to figure out a good scheme to switch between the two output pairs, if you have a controller you could hit both mutes at once, otherwise I am having a hard time thinking how you would just quicly switch on a downbeat
In Pro Tools you can set up two tracks going to different outputs. Mute one of the tracks. Now put the edit cursor on one of the tracks and shift-click on the other so that the cursor is on both tracks. Now every time you hit Shift+M it will switch the mutes on both of them, allowing you to AB instantly. You can also do it by soloing and using Shift+S instead.