Don, of course gain does take place in the output stage(typically 25-30dB), but the point is that the voltage to boost the incoming voltage by that amount comes from the one main power supply section. The output transistors simply act as valves to let through enough voltage to increase the incoming voltage say, for example, 28.28 times so that a tenth of a volt input would result in a 2.828 volt output and into an 8 ohm load would produce 1 watt(the usual speaker sensitivity measurement standard, of course)following Ohm's Law(power=voltage squared/resistance). So an amplifier is a power supply section plus one or more channels of output transistors. The output transistors themselves aren't complete amplifiers, and it isn't correct to describe a 7.1 receiver as having seven amplifiers.
