Axioms are fantastic speakers for both small-budget and big-budget systems. While Klipsch are also a very respected brand, many people aren't fond of their horn-loaded tweeter, which is famous for causing listener fatigue. If the Klipsch model you're referring to is their top-of-the-line, you'll probably find the M60s or M80s to be an easier speaker to listen to, capable of just as much output, and at a substantially lower cost.
Your room is quite large, so you should probably look at something like the Epic 80 package, plus or minus a different sub (there are subs that go louder and deeper, if that's your cup of tea). For rear surrounds, you could get another 1 or 2 QS8s, or the M2 (depending on your preferences for direct- or diffuse-radiating back surrounds).
As far as your receiver choice, Marantz, Denon and Onkyo/Integra all have powerful 7.1 units. 7.1-capable receivers are not mass-market items, and as such tend to be of higher quality than entry-level units. All of them should have a 4 ohm switch on the back. Personally, I didn't like the performance of the Denon 3802 on music, but the 3802 and its successor 3803 have acheived legendary status in the press. Marantz and Onkyo make great products as well, and dozens of people on this board use them.
Of course, if you've got a big budget, audition the B&K receivers, or separates from any of a dozen companies like Anthem, Arcam, Sunfire, or even the budget separates by Outlaw Audio.
Happy shopping!
