Mix & Match, that's what it's all about.
Well the thing is, if you want to have preouts, might is well have them fully unclipped and with a high output (Vrms) for benefiting* by the addition of any external amp(s).
* I was just looking in my dictionary to see if the word "benefitting" took two "t" or just one. Happens that both ways are equally good! Oh well...
I did check for any reviews with the preouts tested on these Yamaha models (865, 765, 665, 565, 465, 863, 663, 563 & 463), and I could not find anything.
But my strong belief is that you need the right amp(s) to match with them, and not any amp, which make things tougher to mix & match.
And anyway, just like you, I don't have any need for this feature. My Onkyos are just fine with my speakers. And if I really want to use a receiver as a pre/pro, I will get the very best at the lowest price, which I already did with my Onkyo TX-SR805. But it just happens that I can also use it's internal amps.
And I know some other people that choose the Denon AVR-2808ci for that very purpose.
I don't think that there are too many people using a lesser receiver as a pre/pro only. Might is well get an Onkyo Pro PR-SC885P, when it was selling for only $529.
At the end, the mixing & matching thing is quite the important piece of the puzzle. Everything, your components (amps, preamps, HDMI...), your speakers, your wife, your room, your neighbours, your tolerance limits and even your pets.
On this, I'll discard myself.
