As you have done the speaker test to establish all speakers are working, then it would seem everything is OK.
Speakers will only output sound that is fed to them from the appropriate Chanel's. If listing to a stereo recording of a song/music, then you will hear sound through only front left/right and base. DVD Movies and games that are intended to give 3,5 6, channel output will do so to to the correct speakers.
If the source is not there to start with, then it will not come through all the speakers, unless you choose, [From your sound card setup] a pseudo effect that will give surround effect even from a mono source. j.