It makes sense comparing Denon AVR-S640H vs Yamaha RX-V683BL because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Denon AVR-S640H has 5.2 versus 7.2 for Yamaha RX-V683BL. Regarding power, then AVR-S640H has such a W/Ohm ratio - 75/8, 100/6 when RX-V683BL has a power of 90/8, 150/4. The THD is 0.08% for the AVR-S640H but 0.06% for the RX-V683BL.
Characteristics of digital to analog converter (DAC) are different, 192 KHz/32-bit for AVR-S640H and Burr-Brown 192 KHz/24-bit for the RX-V683BL. Only the RX-V683BL supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
Both models have the ability to connect to the Internet via WI-FI. Rivals from our review have Bluetooth support. The Denon AVR-S640H has support for AirPlay, AirPlay 2, and its competitor in our comparison - AirPlay. 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-V683BL can receive a content from Pandora, Sirius XM, Napster, JUKE, Qobuz. 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-V683BL 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 6/1 HDMI connectors of the Yamaha RX-V683BL. The HDMI Audio Return Channel (ARC) feature supports both devices. Unfortunately, HDMI eARC is not available on monitored devices. 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. These compared receivers have a built-in phono stage for connecting a vinyl player. It is also worth noting that the ECO mode is presented in each of the receivers. Both AVR-S640H and RX-V683BL can be configured using the Setup assistant.
Only the RX-V683BL has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the RX-V683BL.