Anyone use Koetsu with Harbeth

Which model?

Harbeth 40.2

Real curiosity here and at the risk of sounding dumb... I've never heard anyone ask about a mismatch between their speakers and cartridge. 

Have you heard the Harbeths?  If so, did you like their sound?  What is it about them or your cartridge that you think might not work together? 

I have Harbeth Super HL5 Plus and P3ESR and they sound great with every source I've used with them.

The upper tier of Koetsu cartridges sound different from one another, at least to the point where it would be useful to know which Koetsu you have in mind. The commonly held conception about the mid-range priced Koetsu's is that they produce a lush midrange but lack bass oomph and can seem to sound a bit rolled off in the exteme treble.  Is that what you have in mind? If so, maybe mating such a cartridge with a speaker that had similar character might be too much of a "good" thing, if your aim is midrange uber alles.  But, as noted, that general description of a Koetsu does not hold for all of them, anything above Rosewood level, perhaps.