Ken,
The following thread suggested polk customer service would be best to obtain an answer. Here's the thread...
http://clubpolk.polkaudio.com/forum/...threadid=26523

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?

Thanks!