Regarding your question in the last paragraph, that unit is what's known as the Woofer, made by DW.  It has a microphone built-in, and all you have to do is plug an XLR cable into the mic input on the shell, and you're good to go.

It has two drumheads, and they are tunable.  This unit attaches to your DW bass drum (I think you have to get the mounting hardware for your bass drum if you didn't order the Woofer with your set) and you can adjust the distance which dictates how much the woofer affects the sound.

I don't know exactly, but I'm assuming that you'd mic your bass drum too, probably using the MAY Internal Miking System.  Without a mic in there,  the bass drum would sound funny. :)

The idea behind the woofer is when you strike your bass drum, it causes the heads in the woofer to vibrate, then the mic picks this up, and it causes for a little extra to be added to your bass drum sound.

Tim