There will be some difference given the 804S' aluminum tweeter and Rocehell woofers but if I were going to upgrade, I'd buy the 803S which is much more balanced in terms of bass and overall presence.
I have the 803Ds for my mains and have listened to the 803S and 804S.
I have the 803Ds for my mains and have listened to the 803S and 804S.