Also don’t forget the option to pass unused PC messages in general options so if you set up your Amplitube to respond to PC messages that are not used in GP it should work as well.
Consider though why are you sending those PC messages into your plugin (Aplitube). Most likely you are switching the patch within the plugin.
It is far better and more flexible to create a rackspace for each of your sounds. You get smooth transitions with tail length control and zero glitching in GP if you do it that way. If you rely on the plugin - you could get glitches, delays etc…