I have a pair of 803D for my mains and the HTM3S (essentially a 803S) for my center, DS8S for the surrounds and CCM-65 in ceiling for my rear backs.
For me there is a mjor difference in the diamond tweeters and the aluminum ones in the 803S and 804S. Theya sre simply sweeter and should be for the $1079 cost of each one vs. the $300 cost of the alumnimum ones. Yes, the 803D has more bass and they are perfect for my listening/HT room which is quite large with high ceilings.
Given the right cable, the aluminum tweeters can be not as forward as they are. For any of them, bi-wiring and a lot of good clean power can dramtically improve the sound of any of the 800 series speakers.
The DS8S also have alumnium tweeter which are better sounding than the 700 series and below metal tweeters.
I agree with one of the other posters that mentioned the best bang for the buck is he 803S but I'm glad I spent the money on the 803Ds for both the sweeter and more detailed tweeter and the extra bass at least in my listening area.
I'd forget about the 804S unless you have a small listening area. There is a major difference in bass between the 803S and 804S.