Have you tried downloading an external for OS X compiled as an mxo, and have it unstuffed to a folder, put it in your search path, and have Max tell you it isnt there?
The problem is that Mac OS X isnt recognizing the mxo as a proper bundle, and it shows the mxo as a folder.
Simple fix. Create a file in textedit with this content: “iLaX????” (no quotes) and save it as plaintext. Name the file Pkginfo. Place this file in the Contents folder on the same level as “Resources”.
For example, if you have downloaded the ‘wacom’ object, you’re file structure should be:
Now, rename the wacom.mxo folder to wacom.bundle. Its icon should change. now rename it to wacom.mxo. Its icon should change to anything but a folder (it probably wont be a max external icon.. I get a subethaedit icon). Now relaunch Max, and you should be all set – assuming the .mxo is in your searchpath.