Autosense does not work as expected

I play multiple instruments.  My guitar through the voicelive 2, and my bass through another rig.
When I'm not playing guitar, I'd like to just set the guitar down and let the voicelive be controlled by my guitar player, so here is what I have tried:

I've tried this with Global setting to Autosense.  Global Off, and individual resets with Autosense.

Plug my guitar into Guitar In
Plug my guitar players guitar into Aux In (I''ve already boosted his signal to line level)
Result: NP activated by my guitar.
Set the guitar down, play guitar coming in thru Aux In
Result: NP is NOT activated by Aux In

Unplug my guitar from the back of the voicelive
Result: NP is activated by Aux in

I thought that Autosense was based on listening for a signal and that you could plug multiple things into it at the same time.  For example, a single act with a guitar player and backing tracks.  If not playing guitar, I would have thought the backing tracks would be used for NP.

How can I accomplish what I'm trying to do without buying a bunch of a/b switches to change inputs and turn off the output (I run in dual mono)?

Thanks