I did some researching today online at the CULT OF THE INFINETLY BAFFLED and I really liked the in-wall subwoofer that can be built. From looking at this thing it consists of two drivers, a box, and an amp that is hooked up to your Receiver. Is that it or am I missing something. it looks as if one can be built with two 15" subs for less than $500. Opinions? Testomonials?