standby: 0W (default)
standby: 86W (HMDI Power Control on)
idle: 120W (4 ohm)
idle: 149W (6 ohm)
The Onkyo 876 is Energy Star approved and it consumes less than 1W in its standby (off) state. When the HDMI-CEC Power Control mode is enabled the standby energy usage jumps to 86W which is ridiculous in my opinion. Unfortunately the HDMI Power Control option needs to be enabled for the HDMI TV Control to be active, so you can't have any basic HDMI-CEC controls without wasting a lot of juice all the time. It is best to save the planet, and your wallet, and leave the Onkyo's HDMI control options disabled.
The 876 has an amplifier speaker mode for selecting the either 4 ohm or 6 ohm operation. The 4 ohm option dramatically reduces the amplifier power which was required for UL certification. The difference in idle power consumption is almost 30 watts which makes it a good choice if you happen to have external amplifiers and are using the 876 as a pre-amp/processor.
The TX-SR876 was in an open air rack with good ventilation on all sides and it did not get uncomfortably hot. So the rumors of the Onkyo 876 and 906 having a heat problem are false but I'll have to wait for the summer hot months to know for sure. The 876 did get a bit warm but it was definitely cooler than you would expect from a device consuming 120W at idle.