I find that Personal Orchestra responds uncomfortably slowly on my Mac when played directly from a keyboard. Cathedral organists may be used to this but I'm not. I have found a solution in the use of the free OS X program MIDI Patchbay. This performs much the same task as Apple's venerable Classic Patchbay but, this being OS X, it is easier to use. It enables you to connect any MIDI input to any MIDI output.
First I load GPO Studio. Then I run MIDI Patchbay and create a patch from my keyboard to GPO Studio 1. The improved response is obvious immediately and you can, of course, control it with GPO Studio's Ambiance control. Furthermore you can record your performances in real time. Altogether I find it much more satisfactory.
MIDI Patchbay has been written by Pete Yandell and can be downloaded from: