I'm not familiar with the Polk speakers, but know they make great stuff. I went with 4" Alpine speakers all around. When I put the speakers in, I left out the enclosures in the front. My fairing always seemed to amplify noises/rattles every bump I hit so I covered the entire inside of the fairing and the back sides of the speaker panels with DynaMat. When I knock on my fairing, it sounds solid instead of hollow. This summer I came across those enclosures and installed them and went for a ride. As soon as I got home, I removed them. It sounds so much better without them. The fairing acts like one big speaker box. With the amp I am running, I can hear the radio very well with the volume set at 6...I have Mark T glass packs.
YMMV
What I did was make an aluminum ring with foam rubber on both sides to act as a spacer so I got a tight seal between the speaker and the speaker panel. Otherwise, there is a gap. You can also see how I extended the corners because they are 4" instead of 4 1/2"


