Which AV Receiver?

Get the AVR-X2600H. Plenty of power! No problem with driving your Klipsch speakers! Spending more (2X, 3X, 4X...) will not get "better" sound! Like I’ve said get a smaller pair of Klipsch speakers for the rear. No need for a center speaker (will only degrade the sound). 

The rear speakers should also be Klipsch RP series!

Thanks for your advice roberjerman. 
I will leave the center speak and rears for now and set up the towers and sub with the X2600H.

When I’m ready I’ll do the rears instead of the center. Or is it worth adding both? And yes, will probably get RP series.

Out of curiosity, what will 2x, 3x, 4x get me on the AV receiver?

The guys in the Amp forum recommended an AV Receiver but I don’t know anything about AV Receivers.

Here's everything you need to know about AV receivers: they are crap! Pure, unadulterated, crap. Here's why.

In audio we always face this choice: quality, or quantity. Quality costs big money. Quantity, not so much. This applies to every single bit of it right down to the transformers, caps and resistors in the box. Every single one of which can either sound good (quality) or measure good (quantity). 

So into your receiver box for $399 they have to somehow stuff enough parts for seven channels- seven amps, seven power supplies, seven sets of terminals, plus a dac or processor and God only knows how many inputs. All crammed right in close to each other, in defiance of the fact every one of these things puts out noise that pollutes and ruins the sound of the others. No wonder AV receivers are such crap!

Not to mention, you go the AV receiver/Home Theater route, now you are stuck somehow buying four or five or seven or whatever number the marketers have cooked up this week speakers. So no wonder all the HT speakers sound like crap! They are all being made for and sold to people who care more about quantity than quality.

You can try all this, compare, and this more than anything else is what I recommend: go and listen. If you do then I can guarantee this is what you will find-

ANY two channel integrated amp you can find in your $300-1000 price range will blow away THE BEST AV receiver you can find at any price. Will not even be close. You will hear the difference immediately.

At that point then either you will say stuff it I don't need all those extra channels, they are only gonna force me to listen to crap, or you will say gosh yeah this sounds just mesmerizingly intoxicatingly better but I'd rather have seven channels of crap and a crappy sub to go with cuz won't all my friends and the noobs on the interweb forums be impressed?

Your call. Choose wisely. 

@millercarbon - dude, get off your soap box already!   The guy has a budget of $300-1000 and he wants to add a center channel eventually (which is critical for proper directional sound in movie viewing).  A push to 2-channel integrated is not going to give him what he needs (and yeah, I understand 2-channel integrated is going to sound better for stereo).