Is there a special cable for audio optical jacks?

What are the composite INPUT jacks on the front of a DVR/cable box used for?

• I have a standard Comcast/Motorola DCT cable box -- the big silver one with the bunch of vents on the top. It has composite INPUT jacks on the front of the unit, but I can't figure out if they're usable with the unit's set-up as a cable box, or whether they're not able to be used, just like the USB port isn't. The unit has no "input" selector anywhere on the remote or in the setup menu. Can someone tell me if those jacks are defunct?

• Answer:

  That would be most unusual, since normally the only "input" on a cable box is the coaxial cable from the outside line. Are you certain that they are "input" jacks and not "output?" Most cable boxes have multiple output connections. When I had Comcast, I was able to find the user's manual for my box on the Comcast web site. Suggest you look for yours there--that will tell you what those jacks are for.