I have been trying to use the classic controller with sixtyforce on OS X Leopard, but DarwiinRemote will only recognize attachments to the wiimote as the nunchuck.
Is it possible to use the Classic Controller (plugged into a wiimote) in OS X?
Turns out a fellow 'gamer' has hacked at the DarwiinRemote source and added Classic Controller support himself. Although it is not as tightly integrated as it could have been, it does provide all the functionality that you will need. Just make sure you scroll down to the very end to read all the updates.