Each Sonance digital amplifier includes two Bus inputs with a pass through feature to allow multiple amplifiers to be linked. The Bus A includes a Subwoofer Output with a selectable crossover filter to support a separately powered subwoofer. The Bus allows the output to be looped into a local channel or bridged, and send a high powered low frequency signal directly to a passive subwoofer. The Bus inputs can also be selectively mixed with local inputs for applications like doorbell signal or paging.