Re: 2 mixers into one amp
I've often done something like what Matthew suggested with a matrix DSP. You can either have both mixers always live and mixed together in the DSP or you can create two presets, one for each mixer being active, with a switch to trigger them.
One of the considerations may be whether you have dedicated inputs for each mixer or if some inputs are split, if the inputs are independent than you may want both mixers active simultaneously while if some inputs are split then you may want to avoid mixing or combining the mixer outputs.
I've also used an A&H iLive mixer with one of the PL remotes on a wall or mounted in a rack. For major events you connect and use the worksurface while for simple events you can just use the wall mount remote. You can even program the remote for specific events if you want to do so. The only downside I found is that unless you program it to not control anything then the remote control is live at all times. You turn down someone on stage from the worksurface and they turn themselves back up at the remote. However, I wish some other console manufacturers would offer something similar.