The subs come out as one unit. There are 2 bolts along the bottom and 2 along the top up near the fuse panel.

The first picture here: http://www.xoutpost.com/showarticle-168.html shows the whole box out of the X5. The flat part protuding toward the left side of the picture are where the 2 lower bolts are and if yoy look along the top, you can sort of see the 2 "ears" where the top 2 are.
Hope this helps, good luck!