I like the Bose stereo in the new CX9 but the bass is overpowering in the mid-bass, drowning out a lot of the detail in the music. Adjusting the bass control doesn't do a lot - you either have too much or you have too little by bumping down the control too far.
I had a similar problem in my Ford F150 Sony stereo sub and used a simple remedy to help improve things. The Bose sub is in the rear over the spare tire. I pulled it out and took it apart, undoing the screws that hold the cover plate on, then the screws that hold in the single sub speaker. I put polyfill from a pillow in the space under the sub - not packing it in, just covering all the inside space with a 1 inch or so layer of the polypill. I put everything together and tested it out. While I still have the overly thumpy mid-bass, the polyfill did tone it down quite a bit and cleared up the rest of the music by not overpowering it. The low bass is still there - this affects mostly the drone you hear at certain frequencies. It is not a total cure but it helps. If you are thinking your system sounds the same way it is an easy 20 minute improvement you might like.