It makes sense comparing Marantz AV8805 vs Onkyo TX-RZ630 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Marantz AV8805 has 13.2 versus 9.2 for Onkyo TX-RZ630. The THD is the same and is 0.08%.
Characteristics of digital to analog converter (DAC) are different, AK4490 384 KHz/32-bit for AV8805 and AK4458 384 KHz/32-bit for the TX-RZ630. Both the AV8805 and the TX-RZ630 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 Marantz AV8805 has support for AirPlay, AirPlay 2, and its competitor in our comparison - AirPlay. Spotify can be used on each receiver. The AV8805 can work with the audio stream from Deezer, TIDAL, Pandora, SiriusXM, TuneIn Radio, and the TX-RZ630 can receive a content from Deezer, TIDAL, Pandora. 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 AV8805 can scale the input HDMI signal, unlike the TX-RZ630. The HDR standard - Dolby Vision is supported by these receivers.
The Marantz AV8805 has 8/3 HDMI inputs/outputs versus 7/2 HDMI connectors of the Onkyo TX-RZ630. The HDMI Audio Return Channel (ARC) feature supports both devices. The HDMI eARC is available only on the AV8805. 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.
Each of the AV receivers from our review supports 3 Multi-room zones. The AV8805 supports voice control via Amazon Alexa, Google Assistant, Siri, Josh.AI, and the TX-RZ630 - Google Assistant. An ECO mode is only available for the AV8805. Both AV8805 and TX-RZ630 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.