You would need to select a surround sound mode designed for a stereo input. Try the surround button on the remote. Multichannel DPL2 you have it would be best for movies. 5ch stereo will play all the speakers all the time but won't give your front and rear sound.
If your TV has a digital audio output that would give you digital surround sound. The HTS has coax digital input and most TVs have an optical digital output. You can get a converter to be able to connect them. It will sound better if you do. Check the TV manual on how to use the digital output.