A:Answer The difference is in the number of front firing speakers. As a 2.1 system, the LG 2.1-Channel Soundbar with Wireless Subwoofer and DTS Virtual: X, Model # SL5Y only has 2 stereo speakers (Left & Right) in the sound bar. In a 3.1 system, the Soundbar will also have a center speaker in addition to the two stereo speakers (i.e a center, left and right speakers.) hence the 3.1 configuration. The [.1] is for the Subwoofer...^IFV