After I connect to the CDI device I cannot talk to the connected appliance.

After you authenticate to the CDI device you will see of list of ports that are supported. Each port will show the status of both DTR and RTS. You should see DTR/UP RTS/UP. This indicates that the connected device is presenting RS232 signals to the CDI device. If you see DTR/DWN RTS/DWN , chances are that your cable is wrong or unplugged (or your appliance is powered down).