Yamaha Receiver
FYI,
I have a similar Yamaha receiver (HTR-5860) and it still gets pretty warm after a few hours event though I am using it as a pre-pro. The Emotiva amp, however, is always cool. Also, I wouldn't expect any significant power difference in the Yamaha, Denon, Onkyo, Pioneer, etc. receivers in the same price range.
It takes double the power to produce a noticable (3dB) increase in volume and 10x as much power to double the volume.