I received this email from a reader this week: 

Hi Eric, 

probably that's a stupid question for you but: on MS3 how can I play a VST and an hardware synth (a Roland boutique in This case) on an external instrument track with the same controller without having them playing together but mute the ext track as I'm on the VST. LPX the external instrument plugin solves this, but on MS3 there's no source to choose