I think the greater question may be how much power you have; I can't speak for the 804's, but the 803's need a good amount of power.
There have been many posts discussing the 804 vs. the 803, some will claim the 804 is close, then others, like above, find a vast difference, I suspect this difference is in giving the 803's enough power to really shine.
I have heard the 803's recommended with the Plinius 250 numerous times; I have had the 803's with the Rowland Concentra II and this sounded very good and I have heard them with bridged Bel Canto's, briefly, this is something like 350w a side I believe, and this sounded very good.
Furthermore, I speculate that the first post is accurate that both may work fine in comparable rooms, the 803's may have a bit of an edge in filling a bigger room.
Just my *thoughts*.