The P50 and then the P45 were of course designed to complement the BM6000 (I have a 1970s brochure that has some excellent pictures). They were brought in to overcome SWMBO hostility to 4 large boxes (ie 4 Beovox 5700s) in sitting rooms!
Personally I think they are a much underestimated speaker - they may not look as chic as the flat panel 3000 and 5000 but produce better sound at a lower price!
Bear in mind that B&O could barely give away those flat panel speakers at the end of their time of production! There was a set of passive BV 5000s on ebay recently that fetched £700 (although I notice another pair appear as a buy it now soon after - was the first a scam to drive up the price!)
Brian