That doesn't make much sense since the AVR will run out of steam earlier and start clipping. Just how loud are you listening? I had to run my Q750s (same bass/mid-range as the Q650) to -4db (with music so doesn't always correlate) and full range to get the mid-range driver to misbehave. It was really loud. Well beyond what I would normally listen at.
Also, if you look at the compression data from EAC tests you'll see that neither the C2+ and Q650 are great but the Q650 actually performs a little better over the entire range. At least that's my interpretation of the data.
A few things of note. Yes, home theater can be much more dynamic and demanding than listening to music. I could listen to music all day at even uncomfortably loud listening levels and the KEF speakers would be just fine. With home theater, you tend to listen closer to reference levels which tends to deliver some very impactful extremes.
Also, the only thing my AVR does is decode the audio and send low level signals to my amps. My LCR channels are run by an Emotiva XPA-DR3 amp. 450 RMS watts per channel. I would fry the KEF's well before any clipping occurred. Running separates certainly made for a much more dynamic experience but also found the limits of the speakers. The particular issue was with the Uni-Q driver in the Q650 though I could get a touch of distortion in the Q950's too. If they had designed them with a 3-way crossover it would have solved the issue. But alas, one must step up to the R series to get a three way. $$$ I was not even that impressed when listening to them in the showroom so can't justify the high price point.
As far as the EAC tests go, I suppose it's good to take a look at that but the complexity of real world signals and use makes it hard to know exactly how a speaker will perform in any given arrangement. What amp? What signal? How is the EQ on the AVR set? Listening levels? Etc, etc. I guess sometimes we just have to put them through the ringer to see what happens.
One last thing, my home theater room is what I would consider medium to large for a home. 21'x16' with close to 9' ceilings. With that size you do need to crank it up a bit more.