Using XQuartz for communicating to the Centos server using local graphical user interface
You don't need to switch to runlevel 5, this only means that the server boots into the GUI, not that it's useable. You can use runlevel 3 and launch remote X sessions.

Furthermore, you'll have to use xterm to start the SSH session, not Terminal.app. If you run XQuartz it should open it by default. Then run ssh -X root.website.com to open the session and from this session you can launch the needed applications. If you need the entire desktop, run gnome-session &amp; or your desired VM.

Note that you need to have X11Forwarding yes in your /etc/ssh/sshd.conf.