Im using the Denon X4000 as a preamp because it has XT32 and the Outlaw amp. An argument can be made that Klipsch are so effecient they do not need that much power, but certain things could be used to argue against AVR on board power with a 5.1 or 7.1 system. I like my amp. I looked at Preamps and they are just too pricey when you can use an AVR as a preamp and get an amp. Between my X4000 (open box) and the Outlaw, I have about $1800 in the "preamp" and amp. X4000 is nice also because it has dual sub outs and Dual Sub EQ. It is so easy to eq my subs now.
To me, an AVR or preamp with XT32 is a good thing, I think once setup is ran properly it sounds excellent. The Outlaw amps are good american power and they are rated at all channels driven. My amp is 125x7, but has been tested around 140x7 actual power, and at 3 channels its well up there. So if you have the 7125 like me, and run a 5.1 system, you are actually getting more than 125x5, probably like 150x5.
65" VT50 / BDT460
X4000 / Outlaw Model 7125
Klipsch RF82 II and RC62 II / Hsu VTF-15H (2)
Directv HR44-200 / HR24-500