most difficult speaker to please

The original Thiel CS5 was also a very difficult speaker to drive. Scintillas do seem to be the toughest, though.

Dweller,......Hmm...I currently run a set of Infinity Betas in my system and I don't think they are that difficult to drive at all. I own a set of Kappa 9 and they are MUCH more difficult to drive than the Betas.

Both the Betas and the Kappa 9 need to be biamped.

They guy I bought my Betas from was driving them nicely with two Pass Labs X-250 stereo amps. The Kappa 9 bi-amped with a pair of X-250 will send them crying for their mama.

Mitch4t

Old tubes? I don't know...
I heard this happen at a Stereophile show in Santa Monica circa 1988 (it was a D240 BTW, sorry).
At this same show, I admonished Dan D'Agostino ("do you think those are big enough?") for displaying some rather large amps (Krell? What's a Krell?).
Live and learn...

Of those I've owned:
Ohm F
Apogee Duetta
Apogee Caliper
Bose 901 (original version, Series 1 circa 1971)

Not the most difficult load ever, but, I had a pair of Egleston Rosa's that just ate up a 600 watt Mac amp (602). It's no Apogee but this relatively small speaker had quite an apetite for power.