Infinity Kappa 9, manual request.

There is a fix for you 9.0 was the 9.1 changed the crossover or some such thing. Today Class D amps will push those EASY. Hypex or Ice.
I prefer the Hypex modules with swapable buffer boards. Second the caps in those thing were CHEAP even for the time. 
I've tinkered with 8.0 and RS1B, RS2B, RS2.5s worked on all the XOs
The 1bs had factory upgraded servo bass systems.

All of the ones lest the 8.0 kappa, were EASY loads in comparison
The X.O series were know amp killers because the DIP BELOW 1 ohm
BELOW. Ok! A Class D, Krells, Mcintosh. They work, there are a few more. But for the money Class Ds and hunt for the resistor that causes the problem. Look at  the 9.1 or 2 schemo.  That is how I fixed the 8.0s
I think it was remove a resistor and add a different value, 20.00 fix.

Even simpler yet,  imhififan post a good idea too. disconnect the bass speakers and wire them to a reasonable, 2-8 ohms.  Lower normally = higher THD, ay A LOT MORE. like 5 times as much from 1 ohm to  4 ohm nominal.  PE has a DSP 1200, I use, with great result. More expensive than the 20.00 resistor change, or inductor.. Can't remember, 15 years ago.. BUT there is a fix. Nice sounding speakers, I thought.. Love the old RS series Infinities, I still have quit a few pairs here and there.LOL

Regards

Or, better yet, use a crossover designed 25 years later with better tools.

That's true, however, I afraid not many kappa 9 owner want to abandon the original crossover altogether especially the adjustability.

Or, better yet, use a crossover designed 25 years later with better tools.

They were notorious amp destroyers due to 1 ohm impedance that was not needed.

http://www.infinity-classics.de/technik/manuals/Kappa_9_technical_sheet.pdf
The low frequency crossover is the offender (L12 15mH), use a good subwoofer amp drive the woofers directly (bypass the speaker internal low frequency crossover) can solve that problem.

https://www.parts-express.com/dayton-audio-sa1000-subwoofer-amplifier-rack-mountable--300-811?gclid=...

Consider having the crossovers re-done. They were notorious amp destroyers due to 1 ohm impedance that was not needed.

https://www.ebay.ca/itm/NEW-Infinity-Kappa-7-8-9-Speaker-Crossover-Filter-Network-Kappa7-Kappa8-Kapp...

Hi, jongig.
I believe there is a single manual for all Kappa series speakers.
Can easily be found on line. Just type in Infinity Kappa series owners manual...