How different between B&W 804s & B&W 805s????

"I know that floorstanding speakers always better than the bookshelf..."

Second Brianmgrarcom, Not necesarily true. Mate your 805s to a high quality subwoofer that integrates seamless (e.g. Rel) and you'll get dynamics at least as good as the 804's if not better, and even a fuller sound than the provided by these floorstanders.
Jov

I'd actually prefer upgrading to the 804S over adding a sub, but I haven't had much experience with subs and the little I have had wasn't great.

The advantages of stand mount speakers, usually, is their ability to disppear, at least better than floor standing speakers.

I have only heard the 804S once and I liked it; having owned the Signature 805 I felt the 804S reminded me of the Sig 805's with added weight; I also have a friend that has 804S speakers and is very pleased, he also owned the Sig 805's with a sub, he prefers the 804S.

Brian

I'd save the money..but then again, I am not a BW fan

I have heard the MC6900 driving both and it is a good match either way you go. Both the 804 and 805 are nice speakers. There is something to be said for the two way design and I would not agree that 3 way floorstanders are always better than bookshelves. That is not to say that I recomend not getting the 804. You said you already have the 805 but I would A/B the 804 and 805 at a store carrying both. Audio "memory" is very short lived any other comparison (listening to the 805 at home and the 804 at a vendor) is not coing to help. Also, by listening to both in the same space you will at least have the same acoustic environment in which to make the comparison. Listen to them driven by a mcintosh amp. Keep listening - more than one session - until you know the answer.

The 804s tonal balance is a little brighter and tighter sounding than the 805s. Many have commented on the 804s being a little bass shy but I found a good quality, high current capable amp should alleviate that issue. The 804s do respond well to high quality components. In comparison the 805s sound is a little more rounded and even handed with its well balanced coherence. Depending on your room acoustics the 805 with a sub might be more flexible and pleasing with its greater bass impact. Otherwise the 804s is a good choice if you prefer a two box solution.