Ken - I had the same epiphany a little while ago while I was recovering from a near death experience trying to run a mile under 6:30 (didn't make it either, dammit; 6:34).

The epiphany being that the "amp" per John's description, is the whole process: power supply, transistors, power rails, etc.

But regardless of that, a multi channel system will still need a controlling device to regulate power to each channel's output, dependant to its own discrete input signal.