If your TV has an HDMI-ARC input and you connect the HTS to that you won't need the optical connection too.
Make sure that the TV is set to output in bitstream surround sound. If it was set incorrectly the TV would only output stereo regardless of the content.
Make sure that the content you are watching is not in stereo. If it is you will need to select a different surround mode on the HTS to get the center and rear speakers working.
Did the rear speakers produce sound when you balanced the speaker levels in set up or when you play a DVD? If not then they are not pairing with the main unit of the HTS. Try doing it again. Call Samsung tech support if you need help.
Under normal use the surround speakers won't play all the time. On some content they won't play at all.