He really just needs a decent box, the one he has now is a prefab and you can only modifiy it so much.. I suggested he coat the inside of it with resin, but that will only gain him a few tenths to maybe a half a db. It really needs to be a box designed for those subs and not a generic tuned one.
If he didnt live so far away from me id tell him to come down to the shop and we'll put him on the meter and see what we can do...but he lives in NYC //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif