Since the purpose of the box is to let you try out your mix on different sounding systems,
and probably the worse sounding ones are the most useful in the end,
I wonder if it wouldn't be possible to throw together some different effects on a few busses
and then switch between them for output.
You could quickly set a few obvious parameters per buss that would be similar to different speakers and environments.
They don't even have to sound all that good since what you're trying to achieve is a mix that sounds not too bad on
everything including, unfortunately, an iPhone.