Watch this video. It is hard to navigate GA5 at first, it doesn’t have things where you think they would be. Go to the Kit, as I show in the video, and tag the drop down menu. Here you will find what you are looking for, a listing of all your Kits and add on sound banks. Hm, it seems I can’t load an apple movie here…
Try this: Finding purchased/add-on sound banks in Steinberg GA5 - YouTube
Place you sound banks wherever you want, probably not on your C Drive, and then direct the Steinberb Library Manager to the files. You will see the various headers in the Manager, click on Groove Agent and then direct it to your various kits