You can select which sensors to communicate with using IPSEC.
For Example:
Your director can communicate unencrypted to sensors deployed locally and through IPSEC for sensors deployed remotely communicating over internet connections.
For more information refer to:
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/csids/csids7/unix_cfg/advanced.htm#xtocid2528023
NOTE: When configuring IPSEC use the sysconfig-sensor option for secure communications rather than going through and trying to setup it up through IDM (web based management on the sensor).
Marco