An affordable AV receiver is always a good option to consider, so Denon AVR-S640H vs Yamaha RX-V585BL comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Denon AVR-S640H has 5.2 versus 7.2 for Yamaha RX-V585BL. Regarding power, then AVR-S640H has such a W/Ohm ratio - 75/8, 100/6 when RX-V585BL has a power of 80/8, 145/6. The THD is 0.08% for the AVR-S640H but 0.09% for the RX-V585BL.
Characteristics of digital to analog converter (DAC) are different, 192 KHz/32-bit for AVR-S640H and Burr-Brown 384 KHz/32-bit for the RX-V585BL. Only the RX-V585BL supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Rivals from our review have Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay, AirPlay 2. Spotify can be used on each receiver. The AVR-S640H can work with the audio stream from Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, iHeart Radio, Sound Cloud, and the RX-V585BL can receive a content from Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio. Compared AV receivers retain the quality of 4K/60Hz signal when transmitting from a source to a TV or projector. HDMI signal transmission in standby mode is implemented in each of the devices. The RX-V585BL can scale the input HDMI signal, unlike the AVR-S640H. The HDR standard - Dolby Vision is supported by these receivers.
The Denon AVR-S640H has 5/1 HDMI inputs/outputs versus 4/1 HDMI connectors of the Yamaha RX-V585BL. The HDMI Audio Return Channel (ARC) feature supports both devices. The HDMI eARC is available only on the RX-V585BL. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. Both models support the standard HDCP 2.2. The AVR-S640H has a built-in phono stage for connecting a vinyl player. The AVR-S640H supports voice control via Amazon Alexa, Google Assistant, Siri, Josh.AI, and the RX-V585BL - Amazon Alexa, Google Assistant, Siri. It is also worth noting that the ECO mode is presented in each of the receivers. Both AVR-S640H and RX-V585BL can be configured using the Setup assistant.
Only the RX-V585BL has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the RX-V585BL.