The following thread suggested polk customer service would be best to obtain an answer. Here's the thread...

Here's an excerpt, the question at hand...
Interesting reading. This is definitely another part of home audio that I don't know about. I love it, you guys know everything

If nobody minds I'd like to pose a question. What about the Lsi series? What would anyone recommend for a damping factor on those great pups?

The amp I'm powering my Ls15's has a damping factor of 800:1 @ 100hz with 325watts/channel @ 4ohms. I know there are lots of other pieces that mate an amp well with a set of speakers, but lets just talk DF.
What do ya think?