The Phoenix Audio Quattro can daisy chain up to 15 units using basic Cat 5e cables to make the connections. It can do 8 units using just one power supply (power  from USB just powers the first unit) and then an additional 7 with an additional power supply. 


You can use the MT340 http://www.conferenceroomsystems.com/MT340-p/mt340.htm to provide PoE power to entire chain. Or simply power the 2nd unit with a power supply, the first unit gets power from the USB 2.0 connection.