I was having numerous issues trying to get GPO to work properly on my Mac OS X for a long time but finally managed to get it to operate decently with Garritan Studio, and it hasn't been a problem for about a year. However, I recently decided to switch to KP2, and have had nothing but bad luck ever since.
I went through the whole spiel in installing and authorizing KP2, and it works properly. I can load samples into it and play them on the little keyboard at the bottom. However, when I try to use it with Finale, it doesn't appear in the drop-down list of output devices in the MIDI Setup menu. Garritan Studio is still listed, as is "Finale Output 2007," but there is absolutely nothing related to KP2 to choose from.
I hope I've provided enough information. Any help would be greatly appreciated!