Was browsing at specs of Yamaha A3060. It is sold as 9.2 but supports 11.2. The specs say 11.2-channel processing (up to 7.2.4-ch expandability with external 2-ch amplifier) through additional channel. Can someone throw some light on this? Does it mean that for the balance 2 channels I need a separate amplifier? How do the connections work in this case? There are two ports for rear presence and two for front presence. Does one need to connect a separate amplifier on these?