Good Receivers for Infinity Kappa 7.1 speakers

I would get a used but in excellent condition HT avr receiver that has pre outs on back.
Then you can get a decent sounding two channel amplifier to drive the front speakers/Kappas with.
You can use the HT avr receivers amplifiers to drive the center and rear channels. 

I have their little brothers, the kappa 5.1's and also their big brother the kappa 8.1's

These speakers aren't the easiest to drive and also aren't the most efficient thus I would highly suggest whatever receiver you get, buy one with pre amp outputs.  Then when money is available buy a 2 channel amp to power the kappas, they sound much better this way.  

These speakers aren't the amp killers that the 9/9.1 was, but they still need a bit of juice to sound good.  

I would recommend a Yamaha R-N 803 stereo receiver, with 100 w/ch and able to drive lower ohm speakers they are a good choice.