Red and White connections (RCA) provide for stereo only. For surround sound (5.1), your HT needs to have digital input, connected to TV' or STB' digital output. You might try ARC function on TV and HT, to see whether you can get sound when using other HDMI ports on your TV.
These HT's are design-crippled for a reason. Companies want you to buy higher-end receivers and speakers. With true AVR receiver, everything plugs into it, with TV Being used just as a monitor.