I agree with your logic, so it would seem if 7.1.4 is enough for you and you can't wait, the CX-A5100 would be best, unless you have a specific reason for going with the CX-A5200, such as warranty concern?
If you need 13.1 channels processing, with 15 speakers connected so you can do Auro3D as well then the X8500H is a great option if you can get a deep discount on one. The X8500H has the following pros:
- internal amps you can use if and when you need to.
- has the best measurements among those ASR tested (note: your logic, why not regardless of audible benefits)
the cons:
- Can't do more than 13.1 even though you can connect 15.1 (so you can switch to Auro 3D quickly).
- Bulky and heavy for a preamp processor.
- No XLR, not an issue if your interconnects are short such as 2-3 meters.
AVP/Cs are of course better in theory but in the real world at the moment there just isn't even one that I would touch because I don't see anything that has better audio specifications and/or measured better than the Denon AVRs, let alone real world audible differences. Claims by their users of sonic superiority are anecdotal at best, if not totally not believable. Even if there are some that did measured as well or better, I would still be concerned about paying a significant premium and may do worse in terms of reliability and bugs. For AVP/C/AVRs, I would stick with the try and true brands such as Yamaha, Denon, Marantz or even Sony and Pioneer. I am not confident the boutique brands have the resource needed to support such complicated products, imo they should just stick with amps (pre, integrated, power).