The Onkyo's were known for heat buildup and related failures, but that is easily resolved by good ventilation.
Actually I think this needs to be qualified. I have an Onkyo HT-RC180, sister of the 807. It got hot, even in an open shelf system with 6" space above. Even when pulled out of the shelf and put on the floor with nothing around it, it got hot. Even left on, playing no signal, it got hot.
So I would say perhaps with Active ventilation that is easily resolved, but not with passive ventilation, at least for the 807/rc180.
I switched the speaker impedence to 4 ohm (power wasn't a concern) and turned off the video processing and it ran much, much cooler.
To the OP
The Yamaha Aventage line has a 3 year warranty, the 867 just 2. I think Onkyo gives 2 years for new, 1 year for refurb.
Check the differences between the Yamaha a700 and 800. You might get away with the 700 and save some $.
The Onkyo 709 has Audyssey MultEq XT. That's something to think about.