How old are the 803s? What edition are they? That amp/pre combo will sound good driving the Kantas but better than the B&Ws is going to depend on which model.
Looking at Focal
I'm looking to replace my B&W 803s for the Focal Kanta 3. It's hard for me to travel so can't go listen. What differences could I expect I have an upgraded Carver TFM 45 & a 1070 Rotel pre.