The Kappa 9's are keepers for you whole life.
I have biamped them with a SA/2 from Threshold in the bass and a McIntosh tube in the midrangd and tweeter section and they sound wonderful.
They are pretty close to the RS-1 if powered properly.
Preamp is Audio Research Sp-15.
I must agree about the keeper line. After a comprehensive rehab program I would be really hard pressed to find a better sounding speaker than my K9s. I have tried a range of amps with them and settled with SA/2 Thresholds to drive them. I have done the bi-amp experiments and seem to always come back to these.
I have K7s and K6s and know and have sampled the K8s, I also have the Ren 90s.
When I got the K9s they were in sorry shape. I replaced surrounds, some drivers and still wasn't close to satisfied. In fact, they wouldn't replace my K7s then. But... once I dove into the crossovers, these guys lit up!
Very important with these speakers to replace the big chokes in the low-pass section of the cross-over. These pass most of the current and tend to short as they age. If you find it easier over time to blow fuses on your amps, this is the culprit. Erse makes a great change here.
There are also these pesky little resetting fuses on the Semet and Emits. Change them! Or if you are confident about your power supply bridge them.
But what really made a difference was changing out the caps, all of them. Especially the Solens and the NPE's in the High Pass. I first changed them to an upgraded chineese cap which really didn't change things much, but brought everything into cohession which was sorrily lacking due to the aged caps. I happen to live 5 minutes from Parts Conexxion so I began again recapping, this time with an ear on sonic improvement. Several months and solder burns later I had settled with a majority of Mundorf Supremes with the odd Obbligatto for the film caps and Mundorf E Caps for the 'Lytics. I also ditched the Wonder caps.
Well let me tell you, these guys are freaking unbelievable. Way more detailed, way better staging, no more ssssss from the emits. (Wonder sss). The Rens can hold a candle to them in side by side, even with an Emim vs Poly dome. K9s win in all aspects.
Trust me, if you have the 9s, or 8s for that matter and the crossovers are all original. You haven't begun to hear what these speakers are capable of. Pull the crossovers, buy a glue gun and soldering iron, and hit the mail order audiophile parts lists. if you are willing to part with dough for an amp like a Krell or Threshold, part with another 500-1000 bucks and really do the crossovers right. You'll thank me!