i didn't understand your post 100%, but in effect external switching allows you to control each channel on its own from a source OTHER THAN the original mesa boogie footswitch. For example, suppose you are John Petrucci and have multiple heads and tons of effects racks. You're not going to click on the footswitch for head#1, then hit the button for ch2, and then run over to another set of buttons and hit those to get your reverb and delay. Rather, you have a dedicated unit (such as a bradshaw switching system or a ground control Pro) that allows you to hit ONE button and it changes all of that simultaneously. This is the world that external switching opens up to you. There's lots of information on this sort of stuff. The systems are call MIDI switchers. Just google MIDI for a while and you'll learn a good deal. I learned initially from musicplayers.com. They have a great article on this stuff.
