When installing Audio Unit plug-ins the installer should automatically place the plug in in the correct Directory. However, if adding AU's manually they should be placed Library / Audio / Plug-ins / Components folder. They can be placed in either the System or User library folder. When Digital Performer is first launched after the instalation of a new AU plug in it will initiate a scanning process to load it. If the scanning process fails then the plug-in will not be available.