When a receiver states that it has 120w per channel does that mean all the 5.1 channels? meaning take the two fronts, center, and surround sound speakers and multiply by 5? That would equal 600 watts. I don't think the subwoofer would count because I have it on a pre-out and it has it's own amp. Someone told me that only the 2 stereo speakers had 120watts per channel. I am confused. How do you rate it?