Heres a tip for using gpo in FS. This assumes your working with the way outlined in the FS tutorial.
Say yourve got a gpo instance with eight brass instruments in it. You create the 8 midi out channels so you can write individual parts for each.
Create a Layer channel after the solo midi channels. You can then set some or all of those channels as "children" of the layer. Then, any notes that you play on the layer will play that note on all of the "children" at once. I find this a easy way of roughly writing for a lot of instruments at once or trialing duets between different instruments out.
It doesnt allow any control over mod wheel etc though. Yet. Iam working on that