It makes sense comparing Denon AVR-S640H vs Yamaha RX-V671 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 7.1 for Yamaha RX-V671. Regarding power, then AVR-S640H has such a W/Ohm ratio - 75/8, 100/6 when RX-V671 has a power of 90/8, 150/4. The THD is 0.08% for the AVR-S640H but 0.09% for the RX-V671.
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-V671. Only the RX-V671 supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
Only the Denon AVR-S640H can connect to the Internet via WI-FI. Rivals from our review have Bluetooth support. Only the AVR-S640H supports Spotify. The AVR-S640H can work with the audio stream from Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, iHeart Radio, Sound Cloud, and the RX-V671 can receive a content from Napster.
Only the Denon AVR-S640H has support for High dynamic range (HDR). 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-V671 can scale the input HDMI signal, unlike the AVR-S640H. Dolby Vision technology found support only on the AVR-S640H.
The Denon AVR-S640H has 5/1 HDMI inputs/outputs versus 6/1 HDMI connectors of the Yamaha RX-V671. 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. An ECO mode is only available for the AVR-S640H. The setup assistant will help you configure Denon AVR-S640H.
None of the rivals equipped with Dolby Atmos multichannel audio decoder. The receivers do not support the surround sound technology DTS:X.