The difference between a 2.1 and 3.1 soundbar is the additional center channel in the 3.1 system. A 2.1 channel system includes a left and right channel built into the soundbar with an additional subwoofer. A 3.1-channel system will incorporate a left, right, and center channel, as well as the sub. The biggest perceivable difference will be in the clarity of dialogue, which is typically mapped to the center channel.