But ... it takes many tubes, it would add to the cost. I am not sure how expensive are the tubes ...@gte357s the power tubes are about 27.00 each. In a lot of cases a full set of them for our amps is less than one tube for some SETs!
You will need some power for this speaker. It appears to have a benign impedance curve but if the sensitivity number is real, a 60 watts will be a lot better than 20! A lot depends on how conservative Harbeth is about their numbers- As I recall they are pretty conservative so the speaker is probably easier to drive than the specs suggest.