I've installed PTQ 5.1 and GB10 in a mac with a fresh install of OSX 10.9.5, and I can't see PTQ in GB. I know it's something to do with an AU, but have no idea where to look for it or where to put it when I've found it...

After opening Garageband

•  click on the "i" in the lower right hand corner of the GUI
• then click on "details" in the lower right hand corner
• you should then click on the line that says instrument (down arrow)
• scroll down click "Pianoteq" . .  then be patient it takes a few seconds
•  click on the small "pencil icon" and the Pianoteq GUI will open

After you have opened Pianoteq and selected the preset you want - you may hide the PTQ image by again selecting that "i" icon.

Lanny