I have the Zu Druid Mk4 (although they were originally the Rune model that I had upgraded). Efficiency is 101dB, frequency response 35Hz to 20kHz, 12 Ohm nominal impedance (8 minimum) , 10" proprietary woofer, augmented by a proprietary 1" supertweeter with a split shelf high-pass filter network at 12kHz (as close to no crossover as none at all). Although not quite as low as what you're after, at the price ($2,800) they are a stupendous value. Add a decent subwoofer if you need more low end grunt and you'll be laughing.
I am driving the Druids with 2Wpc of tube power, which replaced 125Wpc of ss (which was also very good), and couldn't be happier. Still require some break-in on the upgraded drivers, but the music is already sweet and satisfying. Very even across the frequencies, mid-range is excellent. Bass is accurate and clean, although not the deepest. A decent sub will fill in the lowest notes if desired.
I am driving the Druids with 2Wpc of tube power, which replaced 125Wpc of ss (which was also very good), and couldn't be happier. Still require some break-in on the upgraded drivers, but the music is already sweet and satisfying. Very even across the frequencies, mid-range is excellent. Bass is accurate and clean, although not the deepest. A decent sub will fill in the lowest notes if desired.