This is my 2nd e53, so I'm not new to them. I'm getting the bugs worked out of this one and I never thought about the fact that some came without subwoofers. I can't see why someone would un-install the factory sub in the last 20 years, so I'm guessing this car came without one. Did the sub only come with the DSP system? If I get a sub from the boneyard, can I just plug it in? Do I need to grab the amp with it? Is there more?