You're wanting the external SD card to be the designated location where TB saves the backups correct?
Like before, hit the menu button then preferences, then backup folder location. Mine defaults to "storage/sdcard0/TitaniumBackup". If you hit the back button it puts me at "storage/sdcard0" and hit the back button again to go up another layer to "/storage". In that folder "extSdCard" would be to folder to store it under. Are you not seeing the external SD card there?