I have had a boatload of trouble w/ my Yamaha RX-V665 not getting enough room to breathe. When pushed it would clip shut down in protection mode and then you would have to turn it on again.I called Klipsch just in case and they scoffed at the idea that model of avr would clip the speakers vs. the avr itself. Now after that disappointment I went out and bought and Adcom gfa555 200wpc power amp and that's what I was using until I went for full seprates.The clear answer is at least 4'' of unobstructed air flow would be sufficient or use of fans. My original set up was in an inclosed rack which was not the healthy thing for the avr.For power amps w/ heat sinks and vents about the same rule applies.
Absolutely ironic some still debate this point...
Heat is the worst enemy of electronics, and with today's packed components with overclocked processors things just heat that much faster....
Additionally with the extreme cost pressures on the products, certain overdesigns that were frequently available are now gone. The other major factors are the loudspeakers, their specs for sensitivity/impedance, room size and what is the average playback SPL..
Just my $0.02...
