I agree with what Johnny Boy said. You will have to check your sound settings on the system to make sure it's not just set to Stereo. There might be an All-Channel setting that will play sound out of all your speakers. But it's just stereo sound. If you want to listen to something that has a 5.1 channel audio source, such as a DVD or Blu-Ray, you will have to set your stereo to Dolby Digital 5.1 to get true surround sound.
I had a JVC TH-M45 home theater system a couple of years back. It had an All-Channel Stereo setting where audio was output through all 5 speakers. And whenever I played a DVD, it would automatically go to Dolby Digital 5.1, although I could set it to 3-Channel (front, center and right) or All-Channel Stereo. Dolby Digital 5.1 is much better for watching movies. The dialogue comes out of the center channel while other sounds come from the other 4 speakers.
My parents had a cheap Coby home theater system that only played audio out from the front and right speakers. The only way we could get audio from all 5 speakers is if we played a DVD on it. Anything else would only play through the left and right speakers, and there wasn't any setting to be able to change that. There wasn't an All-Channel setting either which was pretty useless if you ask me.
So just check your audio settings. Since it's a Samsung (which is a much better brand name than Coby) you should have an All-Channel setting. And if it has a built-in DVD/Blu-Ray player or even an HDMI port, it should play in Dolby Digital 5.1 if you play a DVD or connect a DVD/Blu-Ray/PS3/Xbox 360 system to it.
Good luck!
