well, usually putting a d112 pretty close to the beater gets a nice punchy sound with plenty of low end. having another dynamic in there would creat alot of phase problems. but....a good trick is using a large diaphram condenser outside the kick to get some extra top end click and really low end. also, yeah the hole is for sticking a mic in there. but, you can get better results by taking off the front head to reduce the unwanted ring that is picked up.
