The Pioneers do look better without the grills imo, love the reviews and pricing.
Those Polks should be perfect for the rears.
The reason i went with the Yamaha center was that is wasnt high at all, we only have about 6" to work with height wise for the center channel because it sits infront of the TV. The Polk center might work as it isnt to high. I'll put something on top of the yamaha and see how much extra room we can use