It makes sense comparing Denon HEOS AVR 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, Denon HEOS AVR has 5.1 versus 9.2 for Onkyo TX-RZ630. Regarding power, then HEOS AVR has such a W/Ohm ratio - 50/8, 65/6 when TX-RZ630 has a power of 90/8, 215/6. The THD is 0.05% for the HEOS AVR but 0.08% for the TX-RZ630. Only the TX-RZ630 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. Spotify can be used on each receiver. The HEOS AVR can work with the audio stream from Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, iHeart Radio, Sound Cloud, 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. Both competitors are not able to scale the HDMI signal. Dolby Vision technology found support only on the TX-RZ630.
The Denon HEOS AVR has 4/1 HDMI inputs/outputs versus 7/2 HDMI connectors of the Onkyo TX-RZ630. 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. The TX-RZ630 has a built-in phono stage for connecting a vinyl player. The HEOS AVR supports voice control via Amazon Alexa, Google Assistant, and the TX-RZ630 - Google Assistant. An ECO mode is not present in each of the AV receivers. The setup assistant will help you configure Onkyo TX-RZ630.
Only the TX-RZ630 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-RZ630.