First, what are you using for a foot controller?
if you are using the any ground control from GCX/voodo labs, there will be a parameter where you can store the audio switcher's preset to coincide with the preset of the lexicon. or vice versa.
for exp. when you press (preset 1) of the gcx foot controller, it will switch to (preset 1) of the audio switcher and (the preset you programmed) of the Lexicon.
of course you will need an extra midi cable that will connect from each other's "MIDI THRU"
The lexicon MX2 is pretty cool.
to get the best out of the Lexicon I would the configuration "before the AMP'S preamp and also in the AMP's FX loop.
you can check online for this wiring hook up. But basically you can place part of the LExicon before the amp's preamp and also in the Same amp's FX loop. the lexicon has many ways to be hooked up but i think this more ideal...
if you have a different foot controller that does not have this type of option to store and coincide 2 processors...you would then have to resort to midi bank changes.. where one processor will bring up the other processors' specific preset so that they coincide. I hope i made sense.
I am not familiar with LExicon's MPX 1 ? it too may work like the gcx foot controller.
but read each manual in depth..
Gabriel