The B&W speakers are voiced for SS amplification and are never going to sound their best with tube amplification; possibly with the exception of a pair of Atma-Sphere OTL monoblocks.
Sorry, but I disagree with this statement. I own 804S and when searching for amps I listened to them in the same room and setup with McIntosh MC252 (250W SS) vs MC275 (75W tubes), and preferred the 275. My system has evolved quite a bit since and now the 804S run as active speakers with 400W class D driving their woofers, subs under them, but the MC275 still drives mids/tweeters.
In my journey I veered towards building my own active speakers and looking to drive mids and tweeters with SETs, but doesn't mean good PP powerful tubes can't drive 805 well.
OTLs could very well be it. BTW, thanks Ralph and Almarg for the informative exchange!