i would say, after using various harbeth models now off and on over the last 15-20 years - if i were to have just one amp to drive them, i would select a nice warm sounding solid state unit, in the 75-125 wpc range (i listen mostly to instrumental jazz / vocals / light pop, some r&b - so i value accurate timbre, imaging, top to bottom coherency, clean attack and decay most... )
reason being that i feel harbeths have an innate midrange warmth and texture already, so tubes usually magnify that quality but it is not really necessary, especially if it comes at the expense of bass control and solidity
furthermore, harbeths have a smooth sweet treble, so once again, the classic tube sound profile can sometime cross over into being ’too much of a good thing’ - yes you can certainly excite the harbeth tweeters into harshness, but this is easily avoided
conversely, tube amps that don’t control the bass drivers well enough will result in muddy bass out of the harbeths... which have plenty (except maybe for the 30 monitor and baby hl3) to start with, but sometimes can overload a room and muddy up the midrange if not well controlled
if a touch of tube magic is still desired for the signal chain, i would inject it earlier, in the linestage or dac for instance
my two cents
hope this may help others
