Speakers after Infinity Kappa 9

I'll have to agree with the other 2 members that for me, the Infinity R90's were the biggest and best upgrade I ever made to my system. I also tried the Mirage M1's (not Si's) but they demand space and power so, not practical for many potential owners.
Regarding an alternate speaker with similar sound, I'd have to say that a pair of new Paradigm Signature S6 (v2) speakers I'm listening to - are pretty close. The new pure-beryllium dome tweeter is open and spacious, with no hint of harshness - which is the sound I attribute to the R90's EMIT.

Seems like the VMPS R30's should be high on the list. Can be supplemented with a sub or two.

I had Kappa 9 (original version) Kappa 8.1 and the Polk SDA-SRS all at the same time. The Kappa 9 was the best with airy high and nice clear mid but no bass at all (I used 4 Denon POA-6600 mono blocks for them). The Polks got tons of bass but it was so muddy and mid and highs were no where near as good as the 9s. These were bought just to scratch the itch that I have ever since I heard them when I was a college student. They are all gone now replaced by a pair of Von Schweikert VR4 GEN III HSE and boy am I a happy camper. The bass is just amazing and the mid and high are just superb. It's close to the 9 except that it's much, much, much better. You should give them an audition, you're going to like it.

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Jason, what amp and preamp are you using for the Kappa 9? That might be where your problem lies. The Kappa 9 demands prodigious amount of bi-amped power to sound their best. Min888 said that the Kappa 9 had no bass...the problem in his case was that the amps that he used didn't have the testicular fortitude to drive the 1 ohm load that the Kappa 9 presented to his amps. The Kappa 9 are keepers if you can afford the amplification to drive them properly.
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mitch4t is right, put a class D for the bass and some tube for the high freq.