An audio distribution system in one embodiment includes a master device, a powered speaker unit, and an expander device. The master device has an output port for receiving a cable carrying an electrical power signal along with a digital audio signal. The speaker unit includes a first port for receiving the electrical power signal and the digital audio power signal, and a second port for sending the signals. A digital-to-analog converter in the speaker unit converts the digital audio signal to an analog audio signal, and a speaker driver uses the signal to produce sound. The expander device is electrically connectable to the second port of the speaker unit for providing electrical power to one or more further speaker units. In another embodiment, the invention provides a master mixer device and a speaker unit. The master mixer device includes a digital signal processor for receiving and separately processing a speech channel having digital audio containing speech content and a music channel having digital audio containing music content. In an embodiment a powered speaker unit employing a class D amplifier for reproducing sound is further disclosed. A digital power link in port is provided in the powered speaker for receiving a cable carrying a digital audio signal and electrical power.