I too have a thump in the Mazda from the integrated Bose speakers although it's not nearly as nice as the Sony's.

As I've said in another thread, my Sony has a 12" driver with a 150W amp and I get a nice "thump" out of it no matter where I place it. So driver size has nothing to do with it.

Myrison, do you have the 150Hz amp (ie. does the back of your amp say "by-pass" or "150Hz")?

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated