Bob...I will make it simple.

Take your receiver.....take out the amplifiers and associated circuits, and then you would have a pre-amp/processor. So with your Yamaha, you have the capablity to use an external amplifier and bypass the amplifiers in the receiver.

The advantage of a seperate pre/pro and amp is less "interference" between the two components. And, you can upgrade/change one without having to change the other.

-curtis