Help setting up garritan instruments for finale?

You’ll find Expression Maps for GPO5, along with a Playback Template that works on Mac here:

There’s also extensive documentation about how to work with Garritan and ARIA in Dorico.

If you only have GIFF, then you only need the ‘basic’ GPO Default map for sustaining instruments; and you can use the Dorico built-in Default map for Percussion.