That Onkyo amp looks great for the money, actually. And you could install it somewhere where you never even have to touch it. That's great.
I'm still interested in what the impedance of each one of those ceiling speakers is. Remember if it's 16 ohms you're really only utilizing about half of the available power you're sending to it. But double the power certainly doesn't double the volume. kinda like double the horsepower doesn't double the speed.