A few years ago I upgraded from 804S to 803D because I could not get the bass performance I was looking for from the 804S. I suspect, but cannot verify first hand, that while the 804D bass will be better than the 804S, they are still likely to be slightly lean simply due to physics - the enclosure is not large enough to support deep bass.
Going back to my experience with 804S - brilliant on vocals, but not great on electronic music with decent bass.
On the other hand the 803D has more than satisfied me in terms of overall balance and bass quality. Even after 3 years it still surprises me with how deep it goes. What is also great is that the bass quality is retained at late night low volume listening levels.
So my suggestion is try to compare the 803D to 804D at the dealer to gauge whether the difference in bass weight is significant to you.
Going back to my experience with 804S - brilliant on vocals, but not great on electronic music with decent bass.
On the other hand the 803D has more than satisfied me in terms of overall balance and bass quality. Even after 3 years it still surprises me with how deep it goes. What is also great is that the bass quality is retained at late night low volume listening levels.
So my suggestion is try to compare the 803D to 804D at the dealer to gauge whether the difference in bass weight is significant to you.