My experience so far is that the amp units will generate a fair amount of heat when in use with eco off. Regardless of the speakers plugged in. The unit also maintains a standby temperature that’s around 78-79°f according to the thermostat of my AC Infinity unit. (If power is off completely to the unit, it will be stone cold.)
Given the avr market, there really is nothing I see available, without spending 2-3x more, that makes much difference In performance. So yes, maybe Yamaha runs cooler, and perhaps that is the ergonomic feature that is most important to you, but then I've also seen some people express some disappointment with other features. That said,
@AcuDefTechGuy is a strong proponent for Yamaha.
My room is small, about 2000^3 feet, roughly 11x15' floor space. Without the fan unit on (running Audyssey measurements), I've seen the thermostat get up above 100ºf. Since I use amps on my main 5 channels, the only speakers currently connected to the AVR are the rears. ECO ON helps keep the temp down (as noted previously), and when coupled with the AC Infinity, I rarely see it creep over 81ºF while listening in Stereo. Maybe ~83ºF in full surround.
Some random thoughts: if you want to modify the interior cabinet walls, you could use a hole-saw to cut vent-holes which could have PC cooling fans set up to circulate air inside. You would need to ventilate cabinet doors, too, perhaps... so maybe not the best option.
If you own, you could modify the cabinet doors to have
perforated metal screens added to the front. This would give better ventilation. A powder coating facility could do them up in white for you, too.
More drastic, if you own... get rid of those cabinets.
Of course, I'm a bit of a minimalist, and all I wnt on my front wall is the TV and my speakers!
Good subwoofage will help take load off the amps, and actually contribute, perhaps to running a little cooler. I will always recommend having two matching subs... you do not need the biggest and baddest unless you want.
Hope this gives some ideas for helping you brainstorm some other solutions.
Cheers!