The manual which accompanies GPO states that it is easy enough to have various instruments playing different parts simultaneously. This is accomplished by assigning instruments to different midi channels.
I'm using Logic as my sequencer and am having trouble getting my head around this. A software instrument track can play only one region at a time, how do I have strings playing one set of notes while the timpani plays something else? I could have each on a separate software instrument track, but creating a full orchestral piece would require many separate software instrument tracks and would, then, sap CPU resources rather speedily. I gather there's a way to do this, but at the moment I don't "get it."
Use multiple MIDI tracks, each with a different channel, and route them all to the same GPO-KP2 instance. Each instance can handle 16 midi channels, so it can handle up to 16 instruments on unique channels (you'll see them assigned when you load an instrument). You'll need to load more instances if you go over 16 instruments, but the CPU hit for the second instance isn't too bad.