You need terminasion in both ends of a SCSI chain no matter what controller you use. However some controllers have builtin terminasion or space for terminasion resistors where others don't. If the card have an external port but no external terminator and still work that meens the SCSI chain is already terminated most likely on the controller. If that's the case remove visible resistors (usually comes in 3 rows of resistors) or jumper the board to not be terminated... and then terminate the external harddriver or it's passthourghport.
