Oh, I didn't answer your question in full.
You want comparative analysis:
If you get an AVR alone such as a Denon, Yammy, Pioneer, etc.. all of their power ratings are based on 1 channel driven if that. Without any frame of reference, you would hook up your AVR to your def tech mains and klipsch surrounds and set reference level to 80/85 db or so. You'll be fine but as program material gets intense during action scenes, etc.. your AVR alone will not be adequate in power delivery so the speakers can handle the transients. You run the risk of underpowering the speakers and in fact, speakers can get damaged by the clipping (not enough power) from the AVR. Your AVR alone option would be cool, suffice, adequate.
But keep the mantra in mind for your def techs: All AVRs as a standalone, lack the power your speaker wants, demands, needs, begs, aches for.
Instead, add in either a XPA-3+AVR or XPA-5/UMC-1, your friends, after experiencing the demo of the alien pod in the War of the Worlds or the train coming in 3:10 to Yuma, or Titan A.E. or better yet, the depth charges scene in U571, will go, "Holy Smit!" ... "Nucking Futs!"... "I thought I was gonna die!", the superlatives go on and on.