Just pulled out and stuffed the sub about half full with some poly fill. Is it really necessary to have over 20 torx screws holding it together?! Ridiculous. I think it took longer to undo all the screws than it took for the entire process of removing and installing the sub!

Anyways - sounds a little better. I may put some more in after a longer evaluation, but for now it's definitely less boomy, and there's actual distinction of the lower frequency notes than ever before. Relatively easy mod, completely worth doing.