Add a new IP telephone in the 3300.  Assign it a number, etc.  Under the device type choose "Generic SIP Phone".  Once the device has been added to the 3300, go to the Access and Authentication tab for the device and enter a User PIN that will be used for authentication.
In X-lite go to your SIP Account settings and add a new account.  Include the following:
Username: Extension of SIP device in 3300
Password: User PIN of SIP device in 3300
Domain: IP address of 3300
That should at least get you connected.