Denon AVR-S640H vs Yamaha RX-V4A comparison definitely makes sense.
Considered AV receivers have the same number of channels 5.2. Regarding power, then AVR-S640H has such a W/Ohm ratio - 75/8, 100/6 when RX-V4A has a power of 80/6. The THD is 0.08% for the AVR-S640H but 0.06% for the RX-V4A. Only the RX-V4A 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-V4A can receive a content from Deezer, TIDAL, Pandora, SiriusXM, Qobuz. HDMI signal transmission in standby mode is implemented in each of the devices. The RX-V4A 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-V4A. The HDMI Audio Return Channel (ARC) feature supports both devices. The HDMI eARC is available only on the RX-V4A. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. The AVR-S640H supports the protection of digital content of the standard HDCP 2.2, versus HDCP 2.3 in the RX-V4A. 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-V4A - 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-V4A can be configured using the Setup assistant.
None of the rivals equipped with Dolby Atmos multichannel audio decoder. The receivers do not support the surround sound technology DTS:X.