According to Finale's Expression Assignment dialogue box, it should be possible to generate different dynamics on instruments that are on different layers of the same staff, providing of course that the instruments are assigned to different channels.
But it doesn't work. No matter what you put in that dialogue box, dynamic expressions affect only layer 1. Instruments on the other layers just remain at their default level.
This makes it impossible in GPO to have, say, Violins KS on layer 1 and Lush Violins on layer 2, and have the Lush Violins controllable. The Lush Violins ignore the dynamic markings.
That means the only way to use different versions of GPO instruments in Finale and have playback control over them is the have them on separate staves, which defies orchestral notation convention.
So why is there a dialogue box that supposedly allows one to specify which layer will be affected by playback expressions? It's useless.