I should also point out that the Harbeth Monitor 40 is a 3-way design.... so tri-amp ?
But yes, the woofer would probably still not be (as) happy (as the mid and tweet) with just 16W.
Out of interest, the Harbeth Monitor 40 was designed as a drop in replacement for the Rogers LS5/8 in BBC studios. The LS5/8 was a 2-way design and was driven by a BBC modded QUAD 405 to bi-amp the LS5/8, with frequency splitting and eq performed at line level as part of the BBC mod.
IIRC, Harbeth went on to use QUAD 405's to demo the Monitor 40, one 405 per loudspeaker - I think these would have been wired as monoblocks with the standard crossover in the Monitor 40.
I like the series / parallel idea though Doc ! - the big Kaiju monoblock