Can't you find the Polk LSI's for a lot less? A couple of on-line stores have the LSI 15s, FX, and Center for $1,997. How would the LSI's work with one of the M&K subs?
It's not just the sub that makes the M&K system work so well. There's a clarity and tightness to the M&K satellites, with none of the boominess or slow bass response Polks typically have. Everything is sharp and accurate, and they play LOUD with no audible distortion. They make it sound as if what they do is completely effortless.
I'm sure the M&K sub would sound great with whatever speakers you paired it with though.