As said above...
Your surround system should include digital audio inputs either on SPDIF or Toslink (RCA/Cable or Optical cable). This is the best way to connect your digital devices including digital/HD cable or DSS, DVD, CD, and game system. The digital connection will send all 5.1 channels into the system.
If only using 2 cables, there is some additional surround information that can be sent on those two cables (nothing to do on your end) to provide surround, but it won't be nearly as clean as a digital connection.