A lot of developers create install packages that take care of the heavy lifting when placing plugins in their respective folders. However, some of them only provide with the .aax files along with their .vst and .au counterparts. Of course, some Pro Tools users don't care much about VSTs or AUs, but at least in my experience, if you want to install them all, it is a complicated matter to remember where to place the corresponding plugins. Typically, plugins are installed at these locations:

VST and AU plugins: Macintosh/Library/Audio/Plug-Ins
AAX plugins: Macintosh/Library/Application Support/Avid/Audio/Plug-Ins

Then it'd be useful that all plugins be installed at the same folder, for the sake of practicality, but you know Avid. Practicality is not always at the top of their priority list. Anyway, a way to solve this problem is to create a Symlink in the VST/AU plugins folder to the AAX plugins folder. It is not a complicated task and it only implies the use of Terminal in OS X. A Symlink is like a Windows shortcut; however, unlike Windows, pulling a direct link by dragging it from Finder won't allow it to work at the system level, so it pretty much is useless. Here is the process to create a Symlink for the AAX plugins folder to be placed in the AU/VST folder:

1. Open Terminal (Macintosh/Applications/Utilities/Terminal).
2. Type in the following without quotations: "ln -s"
3. Drag your Avid plugins folder to the Terminal window. It's where the Symlink will point to.
4. Drag your desktop folder to the Terminal window, too. This is where you'll temporarily place your Symlink. At this point, your Terminal window should display something like this (without quotations): "ln -s /Library/Application\ Support/Avid/Audio/Plug-Ins /Users/username/Desktop"
5. Press Enter and quit Terminal.

At this point, you'll see a Symlink folder icon named "Plug-Ins" appear on your desktop. Now we need to rename it and place it in the VST/AU plugins folder.

1. Press Enter once to rename your "Plug-Ins" Symlink to "AAX."
2. Drag your newly renamed Symlink to the following location: Macintosh/Library/Audio/Plug-Ins

That's it. Now everything should look neat. You'll have Components, VST, VST3, and now AAX folders to place your plugins into. If anything gets complicated or if further support is needed, PM me.

Peace.