that and a fan controller should quiet things a bit. htg sells one for $20, I use one of the 6" fans with the controller turned down halfway and it makes a tremendous difference in the sound, plus I can turn it up full speed if I need to. been thinking on one of the mufflers myself. they have a demo video too
Phat's mufflers (http://phatfilter.com/phat-muffler/) use glass pack instead of foam. Should hold up longer and absorb more sound. Fiberglass is often frowned upon but they way they are put together I can't imagine many glass fibers are coming loose and being expelled.