What does a power amplifier do?

More 'real' power translates to more volume. Real power means the ability to provide both voltage and current to drive a speaker (similar to horsepower and torque in a car). The idea is you need an amp that is capable of driving the load of the speaker at the volume levels you need in the room and at the distance you are from the speakers. More than that is good but not useful (do you need a car with a top speed of 200mph or can you get by with 150mph). Too little means that the amp will clip or compress the maximum volume and that can cause distortion. If the amp is not happy with the speaker load it can sound bad at lower volumes.

Then there is the intrinsic sound of the amplifier. This affects the quality of sound at all volumes.

As I have no experience with power amps I don't get everything you said about it, but it looks like you are saying yes it will make moderate levels "better".

However, I would like a simplified answer as my question is fairly simple.

thanks for the reply and thanks for any further replies.