No I did try the Audio Note SORO with the 40.1 which is similar in sensitivity and it wasn't enough (and the SORO has more balls than the OTO - though I prefer the sound of the less expensive OTO over the SORO). The AN E is roughly ten times more efficient than the 40.1 so it sounded far more "alive" with the lower powered amps. Allan Shaw of Harbeth has written that he feels more watts is always better - and for his speakers I kind of see that. Of course the OTO can drive the speakers just as they can drive B&W N801s - but I feel like - if you are going to pay $15,000+ for a loudspeaker you really have to have the ability to play loud with good bass output - otherwise you're kind of throwing your money away on the speakers (and for the matter the amp).
I mean I suppose if you only listen at low moderate levels in a smaller room it "could" work pretty well - the OTO has surprised me over the years at what it can do but still Harbeth just isn't designed for SET amps.
I'd probably look for amps from the likes of Octave, Prima Luna, Melody Valve, VAC, Line Magnetic in the 50ish watt range and see how that works out. From Audio Note - I would really like to try one of the ANKits EL34 monoblocks - 70 watts per channel autobias
pure class A triple C core transformers and not a lot more money than the OTO (but you need a preamp).
Stick these suckers on those Harbeths - I'd like to hear that
http://www.ankaudiokits.com/EL34-70-70watt-Monoblock-power-amplifier.html