It makes sense comparing Denon AVR-S640H vs Marantz SR7015 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 9.2 for Marantz SR7015. Regarding power, then AVR-S640H has such a W/Ohm ratio - 75/8, 100/6 when SR7015 has a power of 125/8, 165/6. The THD is 0.08% for the AVR-S640H but 0.05% for the SR7015. Only the SR7015 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 SR7015 can receive a content from Deezer, TIDAL, Pandora, SiriusXM, Napster, SoundCloud. HDMI signal transmission in standby mode is implemented in each of the devices. The SR7015 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 8/3 HDMI connectors of the Marantz SR7015. The HDMI Audio Return Channel (ARC) feature supports both devices. The HDMI eARC is available only on the SR7015. 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 SR7015. These compared receivers have a built-in phono stage for connecting a vinyl player. Supported voice control technologies are identical - Amazon Alexa, Google Assistant, Siri, Josh.AI. It is also worth noting that the ECO mode is presented in each of the receivers. Both AVR-S640H and SR7015 can be configured using the Setup assistant.
Only the SR7015 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the SR7015.