How to read speaker sensitivity rating?

Sensitivity, like most other specs is somewhere between misunderstood and meaningless.
Without some other information, like some idea of maximum power handling and phase angles at frequency, sensitivity is just another number to hit back and forth over the net.

If your 100db sensitive speaker can handle 20 watts before the smoke gets let out, that is a much different animal than the same speaker with a max power handling of 400 watts.
Likewise for phase. If the speaker were a (mythical + flat) resistive load that would be a completely different kettle of fish than a similar sensitivity with a 3 to 20 ohm range and some wacky phase angle at the impedance minima.

By itself? Sensitivity is not worth much as a single number.

The Kappa 9's, when used with their "extended/normal" switch in the "extended" position (which iirc seemed to be the most commonly preferred setting), are conceivably the most difficult speaker load ever devised by mankind, at least among home speakers.

In that mode they go down below 0.8 ohms at multiple bass frequencies, where lots of energy is typically required. I know of no other speaker that comes close to doing that, although I believe the Kappa 8's are not too far behind. The "normal" mode is not quite as severe, but still very challenging.

I don't know what their phase angle behavior is in the bass region, but it wouldn't surprise me if it was significantly capacitive, adding to the severity of the load.

I can't imagine that a Zu speaker would be anything like that.

Regards,
-- Al

The Zu's would be a much easier load for your amp.
And the Dominance is a dream speaker. I envy you.
You will also love the crossover-less design of the main drivers. They should be a move in the right direction for you.
John

Will someone please explain "phase angle"?