I can't get the GPO to recognize my midi controller, which is a Tascam US-224 mixer, which goes USB into my computer. I have no options in Garageband for inserting the plug-in's so I was trying to find out how to use GPO with Garageband and a mixer/Midi controller. The input and output windows in the "Midi" section of "Audio Setup" are blank. I appreciate any advice. Thanks,