Which GarageBand '11 version do you have? I'm puzzled by "New Update". The last GarageBand '11 update (GarageBand 6.0.5) has been released in May 2012 .
In all GarageBand '11 versions you add Audio Units from the Info panel in the "Edit" tab.
If you are using the newer GarageBand 10.2, you add the effects and Audio Units from the Info panel in the Smart Controls for a track: Click an empty field in the plug-in section.