I run 804S with a McIntosh MC275 and love it. The 275 definitely has no trouble driving the 804S. For the 803D, however, you might need/want MC275 running in mono, so 2xMC275, and short runs from amp to speaker would help even more.
I've heard 802D driven by $30k VTL monoblocks and $20k pre, and let me tell you...boy can tubes drive B&W!!!! Mayeb a little more expensive than you are looking at spending, though, but the point is tubes and B&W 800-series CAN sound VERY good. Just a matter of finding a good match.
Sorry I saw this post 2 weeks after you post it.