It will still play if your television is set to use surround, but to get the full effect of 5.1 you would need to buy a LG set of rear speakers. I bought this from Best Buy:
LG - Powered Wireless Rear Channel Speakers (Pair) - works with select LG soundbars - Black Model: SPK8-S
After a few days, I felt I needed the rear speakers, and the sound bar wasn't enough. The rear channel speakers are easy to install. Plug them in and your sound bar will instantly recognize them.