My Marantz AVR running just as a pre-pro in low energy mode (the amplifier channels are not connected, ECO mode is engaged, and only L/R speakers are defined), and the AVR still dissipates more heat than the ATI AT602 amplifier it drives. I'm guessing there are several line-level op-amp ICs and DAC ICs running in a static-level power mode contributing to the surprising BTU output. One of these days I'll stop being so lazy and download the schematic, but my Reed Instruments power meter says a pretty consistent 36 watts while playing 4K video from the Roku box to the display and stereo audio to the amp. It runs hot enough to need a fan in the cabinet.