All five speakers should never play all at once, but should only play when a source is directing audio to them.
Most cable boxes have a setup option which allows for you to set it to stereo or surround, which can make a difference.
Will you please specify if your cable box is connected directly to the TV via HDMI or is the cable box connected to the A/V receiver via HDMI?
I would think that it may be a cable box setting, and you want to go into SETTINGS->SETUP->AUDIO on the cable box (somewhere) and make sure it is set for surround sound.
Generally most audio from things like the news comes out of the center speaker.