I replaced my LSi25 subwoofer with Polk MM1040UM and listened to it for the first time last night. I can say that I am very happy with the results. I listened to The Battle of Kerak and I felt vibration from the floor and sofa where I sit. Then I listen to some pop beats and it really filled where the upper drivers left off with solid bass.
This is just my first impression and it is only from one speaker as I've not done the other one. In my plan I have prepared that I might have to modify the stock port to 4" x 26" (more data about this at a later time) but it seems I may just be satisfied without that extra work.
I need to do more listening as it requires 20 to 30 hours of break-in according to Polk and re-adjust my settings when I have my other speaker done. There are other detail information I will provide but just wanted to share this quick news for now.