Technically, you don't need poly fill or foam in a ported sub. Many guys use it in sealed enclosures to trick the driver into thinking its in a larger enclosure. You're better off to dampen the room, rather than the box itself in a ported enclosure. My sealed enclosure in my truck is stuffed 70% with poly. It makes quite a difference.
Wow, $6000. That's one big home. We replaced ours a few years ago for $750, but it didn't include the furnace. Our home is only 2400 sq. ft.