Do you currently own the 805S? I was wondering if they are 8 ohm or 4 ohm. The B&W specs say they are 8 ohm but I hear people say they are closer to 4 ohm.
The impedance varies quite a lot but I think they remain at 8ohm or higher mostly and short dips down to 4ohm or a little less should be ok for most
good receivers. A friend of mine used a 20W tube amp for a while on his 805S and now uses a 30W Naim amp so you shouldn't worry about it - they are much easier to drive than B&W's previous models.
I use a 4306 receiver with my front pair of 804S - using 4 channels biamped (

yeah, I know) - and I don't think I ever get any where near clipping and they sound better than fine

. But having said that I’ve just received (this afternoon!) a HTM3S center that I plan on using with an external amp (a Bel Canto monoblock) as that supposedly gets down to 3.2ohm and I didn't want to risk stressing the amp in my receiver too much with that extra load - and I'll admit that I just love the kit for its own sake.
A word of advice; let your wife have the 805S, if you don't you won't ever hear the end of it.

(I'm thinking about getting a pair for my surrounds next year).