Newbie could use amp, receiver help.

More,4 ohm and 8 ohm impedance.A 4 ohm speaker is twice as hard to drive as a 8 ohm.It sounds backwards,0 ohms is a direct short.

If you use an A/V receiver,make sure that it can drive a 4 ohm
speaker load continuously (same for power amps)into a stated
XXX watts into 4 ohms continuous watts RMS. The standard for A/V receivers is 8 ohms,although a lot of A/V receivers can drive a 4 ohm load.If you use (5-7) 4 ohm speakers, thats a lot of heat for a receiver.Infinity states the amp must be able to drive a 4 ohm load.The Infinity's will probably not match the sound characteristics the Klipsch's.You will want all the speakers in a home theater to sound as similar as possible. Getting sonically matching speakers may be hard? If you like the Infinity's sound for a 2 channel(stereo)system,you could keep running the Klipch's for video with a A/V receiver that has preamp level outputs for the front channels running them to a 4 ohm capable power amp.That would give you Klipch video sound 5.1-7.1 channels,and 2 channel stereo
for the Infinity's.Or match up all Infinity speakers FRT,CTR,and REARS, for it to sound right.All that said,if you go with the Infinity's,use an amp that will drive a 4 ohm speaker continuously. I would want an amp of at least 100 to 200 watts (myself) into 4 ohms for the Infinity's (the 4 ohm is very important).If you try using an 8 ohm only amp,it will most likely be damaged,and may damage the Infinity's too. Go to Infinity's support sight and look up the owners manual.I hope this helps.

A decent AVR will do the trick. A used one with the new hi-rez codecs. I like and use an Onkyo TS-SR905.

Logically, you are going to need a power amp and a preamp. You can purchase a HT receiver, which combines the power amp and preamp or you can purchase separates or a combination of the two approaches (for example, use a HT receiver as a preamp with a power amp).

If the Infinity Kappas are power hungry (and I am taking your word here), then whatever you do, you will need a power amp that delivers a good deal of power. Since so much of the power used is consumed reproducing the lower (bass) frequencies, you can also purchase a powered sub-woofer which is nothing more than a speaker designed to reproduce the lower frequencies combined with its own amplifier, so it takes some of the load off of the HT receiver or power amps.

With me so far?

The situation with many lower cost HT receivers is that their power specs are misleading. The power specs are quoted only running one channel or
at one frequency point (i.e. 1000hz). So you will need to find a receiver that is rated for high power across the frequency range, with all channels running.

I will leave it to others to recommend brands of receivers. It is more than just the watts though ... size of your room, how loud you like to listen, how much you have to spend, etc all comes into play.

Good luck,

Rich