Have you gone through the thread linked below yet? It is 69 pages long but if you will get a lot of opinions and many listed facts, pictures and graphs. When you are done you should be ready to make an informed decision.
From my own experience, as HD mentioned, there is no audible advantage going the pre-pro+amps vs AVR or AVR+amp routes especially, as ADTG mentioned, if the pre-pro is simply a AVR minus the amps, plus the XLR circuitry and connectors. To summarize:
Argument for AVR based pre-pro (e.g. AV770X, AV880X) - Less components/parts in one box, easier to manage heat, have balanced (XLR) connections and legacy connections that some people may want to have. If failed beyond repair, you only have to replace the pre-pro. On additional plus, is that you can pretend it sounds better. In fact, with the power of expectation bias, a lot of people don't need to pretend at all!
Argument for AVR, or AVR+amps (if you really need the additional power or channels) - Everything in one box, so only need approximately half the space. Without the legacy and XLR connections and the associated wiring, by making the box slightly larger, better ventilated top, additional of fans, and now the improved Eco mode, additional heat does not seem like an issue any more. With Eco mode set to "On", my X4400H, that replaced my AV8801 actually runs cooler, though warmer if Eco mode is "Off" or "Auto". In terms of reliability, it is hard to compare because the AVR has more things that can fail in one box, while the AVP+amp has two pieces that can fail, and the AVP+amp actually have more components/parts combined, than the one piece AVR.
Two additional advantages of the AVR/AVR+Amp options:
1. Price - As an example, you can now get a SR7012 for $1,000 below the list price of $2199, because the SR7013 is out, that is a fantastic deal compared to the price people were paying only a couple of weeks ago. Or $899 for the AVR-X4400H that is virtually the same as the SR7012, minus the silly HDAM (Marantz), plus the so called AL32 (Denon) and the legacy mult-channel analog input that few people need or bother to use. Outside of North America, the price gap between the Denon and Marantz is less than half of what we see here.
The point is, you can always wait one year and get a super deal for a brand new flag ship or near flag ship AVR for half the list price, that is not the case with pre-pros, not even the AVR based pre-pros.
2. With AVRs, such as the SR701X series, you get 9 channels of amps, so in additional to being a back up to the power amp, you also have the option to use the internal amps to power the less demanding channels, and spend the same amount for a 7 channel power amp on a more powerful 3 or 5 channel amp instead. For people on a tight budget, that could be a big advantage, especially for those who want to take advantage of the AVR's 11 channel (such as going full blown 7.1.4 Atmos) processing capability.