I've had both relatively recently for extended periods (purchased the 804S lived with them for about six months and then upgraded to the 803D lived with them for about six months and have now moved on) and it's not even close. The 803D is in a whole other league - the diamond tweeter, the midrange transparency and the bass. If you have the funds, don't waste your time auditioning the 804S. Frankly, the 803D is where B&W starts.
