Two independent sub outputs, with the most important difference being the ability to have variable delay between the subwoofers. Reason being if your Outlaw LFM - 1 Plus is 4 meters from you and your sitting on your bass shaker or hsu MBM, there is going to be a lag of 0.01 seconds. I suppose that is not very perceptible, but so much of this hobby is the imperceptible, right?