Well, the thing is, the pure, unequalized, uncorrected power will be the same whether you go with Marantz / Denon, Pioneer, Yamaha, Sony, and so on. (There could be a smell of ozone when an Onkyo fries, but that's a different matter.) The real question is, do you prefer Audyssey, MCACC, or YPAO for eq / room correction? Yamaha fans say there's nothing better than YPAO. Pioneer fans say there's nothing better than MCACC. I say there's nothing better than Audyssey. Unfortunately, I've never come across any posts from anyone who has owned more than one such technology, who has had the ability to provide graphed measurements to demonstrate the effectiveness of each.
I can say that Audyssey XT on my Marantz automatically corrected my bass pretty closely to my tedious manual corrections. The Dynamic EQ feature introduces a house curve (loudness) at low volumes, but flattens out as reference volume is approached.
Science. One has little control over the slope of that house curve. Nevertheless, the Audyssey scientists picked a pretty good curve, and dialing in your preferred amount of bass via the LFE channel volume control works without sounding unnatural.
But if I had it to do over again knowing what I know, I'd probably get the X4000.
For what it's worth,
many of us have gotten refurbs from A4L, and no one seems to have experienced any notable problems. My Marantz is an A4L refurb, and I honestly wouldn't have known it was a refurb if someone else had done the ordering, save for the refurb labels on the box.