Thanks for the links / pics!
(1) I didn't know the HPM was a Piezo!
Not having a stellar experience with BIC horn-loaded supertweet elements, but used to be happy with Sennheiser HD414 piezo headphones.
(2) I'm listening now to HPM-1500's on a Luxman R-117 and the highs are smoothed just fine.
This 1500 has a smaller radiant surface area than the 200's multi diameter barrels, but has a top-mounted 270 degree dispersion supertweeter driver element; big step up from the 100's I tried. It doesn't pair up nicely with Adcom 555s. Likes Onkyos.
tubed that M-85 is a high-bandwidth design, nice.
In that price range I'd try a couple of 250+ wpc VFET Sonys, MOSFET Haflers, or Parasounds (the larger ones not the half high ones). Let them warm up before passing judgment!
Pro amps with Class-D (if you're okay with switching) will give you plenty of current. Helps if your circuits can handle 20A.
And of course your PRE is more important than your AMP... :scratch2: