Sure you could. It’s just an illogical way to manage the mixer, that’s all. Why should switching one section of the mixer on disable another section? It doesn’t make sense when you’re unrestricted by any physical size - which is why this system isn’t applied to other such choices (eg. displaying MIDI channels doesn’t automatically hide audio channels, for instance; and recently changes were made so viewing inserts and sends was possible simultaneously.) I don’t get the need for all these different windows - the timeline + mixer + instruments paradigm pioneered by Steinberg is a pretty good one after all 
Thanks Alexis, for a sensible suggestion btw. Ideally I’d prefer to have level-matched mono in a single speaker. Not found a plugin that does that yet, but I’ve not looked that hard. I must look again or maybe knock something up in Reaktor, Metaplugin or some such…