Replying to Sound Equipment - HiFi Subwoofer

So I'm looking into a new sub that will match my speakers, I currently have two B&W Diamond 805's. I love the things to death but they've turned me into a bit of an audiophile, and right now I'm rockin a 150W sub with an 8" cone, and really want something that can match the 200W per channel that I'm throwing on the B&W's. I have two options, either A. Buy a subwoofer from the likes of B&W, Klipsch or Velodyne or something expensive as hell, or B. Build a subwoofer myself with relatively comparable specs for about 1/3 the price. The only problem with that is, does anyone know how great the components like the amps are and stuff? Because I'm also not going to be building a shitty trunk styled car sub that's just loud - I'm looking for fidelity. I'm really kind of new to that whole field. Sorry for the rant, but hopefully someone knows at least something? I really don't want to join audioholics or some shit like that