some of them would be incorporated into the speakers, plug in the power supply and go. a good example are sonos speakers i think.
others are 'wireless' - you dont have a wire directly connected to your source or avr, but have to go thru the socket, ethernet, or 'wireless' via transmitter. polk would have em, (again only an example)
to go a step further, others would be using a transmitter to get the signal from the source or avr, then sent to another transmitter, then you choose to use it directly into another avr and/or amplified speaker. ergo, more wires than two. :angry-banghead:
i use this for a wireless subwoofer setup, if i wanted to move my subwoofer around without wiring it due to location...