The "top secret type driver:"
"The core of the Harbeth sound is the exclusive RADIAL™ driver technology" found in the H40/40.1's midrange driver, see:
http://www.harbeth.co.uk/uk/uploadfolder/m40t_a_s.pdf
If you want to sit on a stool like REG, see: http://www.regonaudio.com/REG%20Listening%20Room.html,
and the rest of the Harbeth nearfield marching band, you just found your perfect speaker.
Since I doubt TONEPUB will provide any measuremnts in his upcoming rave review, I suggest you look at the JA's H40.1 in room measurements. Red curve-AD's room. Blue curve- JA's room.

And your point?
JA doesn't know any more about measuring speakers than I do.
He does not have any formal training in electronics, engineering or acoustics.
As I recall the people at Harbeth were in disagreement with JA's measurments
of their speakers, which were measured professionally at the BBC's laboratories.
Neither we nor Harbeth said anything about a "top secret driver".
I like the Harbeths a lot. I'll tell you why I like them in the upcoming review.
If you feel intrigued enough by the review to investigate for yourself, you will
have to decide whether you like them as much as I do. If you do, buy em if
you can afford em. If you don't, continue on your quest for the speaker that
makes you happy.
I suspect, just like any other speaker, you will listen to them and respond one
way or another, as you would with any other thing that you have purchased.
If there was one way to audio nirvana, there wouldn't be so many choices.
And I think you might be surprised at just how much detail the Harbeths DO
provide, given the right electronics. I've now tried them with about ten different
sets of amplification from the Red Wine Audio 30.2's all the way up to a CJ premier
350.
I've also tried them with about six different sets of cable as well.
If you haven't heard the speaker in your room with your gear, you really
don't have much to comment on. Every component made has its set of
compromises, I particularly like these and could easily live with these for good,
especially in a small to medium sized room.