Electronics for Harbeth, Especially Monitor 40 series

Maybe it's no coincidence. Perhaps a pair of Job mono amps would be the poor man's equivalent. Harbeth dealers generally seem to pair them with British integrated amps, and I know that Vinny Rossi shows with Harbeth, but those both sound very different from fast solid-state.

Try Chord or Exposure separates; both would count as "fast." 

Naim would be worth a try also; but you'd probably need a 282/HicapDR/250 combo. 

I've heard all three run big Harbeths (and Spendors) very well. 

I don't have the big Harbeths but for my office system P3ESRs I am using a Rega Brio-R, Apollo-R, and a DAC-R.  Works well together.

Someone had large Spendor monitors with Prasound JC1s & JC 2 Pre, at the RMAF. I thought it was a very good room. It did have very high end analog source material though.

I understand fully why dealers pair them with British amps. That have sonic trademarks typical of British sound generally, speakers, amps. Harebeth being one of the biggest standouts. And they love amplification that share similar attributes, naturally. Something that shares and further brings out there strong points, as with anything else. LFD, Sugden, Exposure, Roksan. Someone coined PRaT and it stuck for good reasons, real reasons. Reasons I dont stray too far away from British sound, or away from at all.