Agreed but having compared the sound quality of the Denon Upgrade with the standard unit I didn't think it was much better. The better (only) option To improve the bass is an aftermarket small powered subwoofer. I had a fairly basic kenwood one installed, £200 all in, and the results were spectacular. They're very small, designed to fit under the front seat. However with all the paraphernalia under the ds4's front seats there's no room there, so I opted to have it fitted on the carpet just below the back seat. It's easily removable if I want an extra back seat passenger (though surely nobody that buys a ds4 gets it to regularly carry people in the back!?). Alternatively it can go in the boot, and it's smaller than the Denon subwoofer.