Al (Almarg) is right Fartman. You need and amp that will deliver big current, which means one that can almost double it's wattage from 8ohm to 4ohm to 2ohm. This means BJT (bi-polar) output stage solid state type amps, with big power supply, eg: old big Krells.
Because the Kappa 9's go down to .7ohm in the low bass and .8ohm in the upper midrange. And if there are any bad negative phase shifts in these areas those impedance figures will be even lower.
This means Tubes and Mosfets need not apply to drive these successfully.
Cheers George