The recommended USB to DB9 cable is one with the prolific pl-2303 chip on it. It is supported by all the Operating systems and works flawlessly. You would need to download the latest prolific driver from their website and install it.
You could use the SecureCRT from VanDyke or use the free version of PuTTY on Mac. To install PuTTY on any Mac, you would need Apple's Xcode installed than download MacPorts and follow the instructions to install the app. When MacPorts is installed, it is suggested to update it by running the command from the terminal:
sudo port -v selfupdate
After the update is successful. install PuTTY by typing the following from the terminal:
sudo port install putty
This will install all the necessary apps to run the PuTTY in the X windows mode. After the app is fully installed, all you have to do to run PuTTY is to issue the command from the terminal like below:
Now, connect your USB to DB9 to your Mac and the Console cable to the router. Launch PuTTY...