About 6 months ago, I put polyfill in my PSW1000 and removed the port cover in the back, and really liked the effect it had. It reduced port noise a great deal and gave it a hair more accuracy. Last night I went ahead and did it to my LSi25s' subwoofer chambers and am liking it even more. They sound a little smoother, and sound like they have less coloration due to any internal resonances. I had all this polyfill sitting around for when I was going to redo the enclosure in my Yukon, but that's gonna go bye bye, so I decided to stuff the 25s.
I'll keep you guys posted as I get more listening time in.