Infinity Kappa 9's Tweaks?

As a current Kappa 8 owner everyone is giving you good advice. These speakers should not be used with Monster cable bi-wire. They just sound awful. However, they do work well with MIT cable, Slima cable and the old Tara Time and Space.

These speakers love tube power. They also like amps that can be driven into low impedance loads. The Odyssey monos sound good with them. The PS audio HCA-2 sounds good with them except beware the tweeeter can get hot if you play them loud ( think the amp is a little underpowered). Older Thresholds are also good. In my opinion most Japanese amps need not apply (except Stax). The Japanese amps are either too bright or can't drive the impedance. The Marantz Ma700 sound good with them.
I would also think the Innersound amp or a Classe would work well.

You might also try taming the wall behind the speaker with a Persian rug. Also stabilize the base. I use 50lbs. of sand on each speaker.

I wound up getting a Sunfire Signature 7, which seems to power the 9's without any strain, very sweet, have a room about 15 ft deep by 14 ft. wide; I wired the amp in current mode, sounds smoother that way. Use Kappa modulus, 2 pair for rears, plan to change to Kappa 6 if I can get them reasonbly. Like to get the santos rosewood cabinets in Kappa 6 if they made that option as my 9s are rosewood.
The Sunfire was also a good price. Handles low impedance no problem.

I also plan to get another Sunfire amp, this time stereo, and run it with an electronic crossover on the 9s. More control that way. The Sunfire puts out about 800 watts into 4 ohms,way more into 1 ohm, without protest so far.

Try a tube pre-amp along with your solid state power amp, you won't be disappointed. The "harshness" in the tweeters is your solid state pre-amp. I have run the Kappa 7s for years with a Conrad Johnson tube pre-amp into a Denon 200 watt amp and they sound great.