@itzhak1969,
Not all B&W speakers require lots of power. I’ve owned their 6, 7 and 8 series speakers over the years. You should do your research before generalizing a brand that makes a wide range of speakers.
Big speakers usually performs better when they are fed with decent power. The 800 being their flagship speakers ‘designed’ to be driven by a high output amp. You don’t feel the need for a sub with 800’s, plenty of low bass with fabulous mid’s and high’s from a pair of speakers once they are setup properly :-)