It makes sense comparing Onkyo TX-RZ840 vs Marantz SR7015 because they both are able to give some premium features.
Considered AV receivers have the same number of channels 9.2. Regarding power, then TX-RZ840 has such a W/Ohm ratio - 180/6 when SR7015 has a power of 125/8, 165/6. The THD is 0.08% for the TX-RZ840 but 0.05% for the SR7015. Both the TX-RZ840 and the SR7015 support Bi-amping. 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 TX-RZ840 can work with the audio stream from Deezer, TIDAL, Pandora, TuneIn Radio, and the SR7015 can receive a content from Deezer, TIDAL, Pandora, SiriusXM, Napster, SoundCloud.
Both AV receivers support HDR10 technology (High dynamic range). HDMI signal transmission in standby mode is implemented in each of the devices. The SR7015 can scale the input HDMI signal, unlike the TX-RZ840. The HDR standard - Dolby Vision is supported by these receivers.
The Onkyo TX-RZ840 has 7/2 HDMI inputs/outputs versus 8/3 HDMI connectors of the Marantz SR7015. The HDMI Audio Return Channel (ARC) feature supports both devices. HDMI eARC is available in each model. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. The TX-RZ840 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.
Each of the AV receivers from our review supports 3 Multi-room zones. The TX-RZ840 supports voice control via Google Assistant, and the SR7015 - Amazon Alexa, Google Assistant, Siri, Josh.AI. An ECO mode is only available for the SR7015. Both TX-RZ840 and SR7015 can be configured using the Setup assistant.
Both devices have support for Dolby Atmos multichannel audio format. The surround sound technology DTS:X is supported by devices under review.