Well, The Polks come with an in-line crossover. It is possible that going to a different brand, other than the Kicker/Subaru upgraded tweeters may not work out so well. The Polks MAY have a higher crossover point on theirs.
Im only saying this because the factory tweeter is a 2" model, which stands to reason they can use lower crossover frequencies.
You can play on the safe side, and install 2" full range drivers like I did, with no crossovers. I believe Mine were only $32 each, or something like that.
Upside to it is it pulls some of your lower midrange frequencies up high on the dash, and plants your soundstage right up there where you want it.