I have been pretty happy with the Image Dynamics in my Old DD. They sound better than the JL's they replaced. They are not the SQ line, but the basic ID line and have impressed me. In my GXP I read up a ton and ended up with an Infinity Kappa. It does not require a ton of power to run. I believe I have a 500W Alpine amp running it. It can hit hard, but the sound is very good and has impressed me. The bang for the buck certainly is there. I am sure there are better subs, but they will likely cost more.
With the back seat up, the quality of sound is muffled. I have been toying with cutting a hole in the middle of the package tray and having it fire directly into the cabin. I haven't really done much of any planning though so I can't help much there.
