It makes sense comparing Onkyo TX-NR555 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, Onkyo TX-NR555 has 7.2 versus 9.2 for Onkyo TX-RZ630. Regarding power, then TX-NR555 has such a W/Ohm ratio - 130/6 when TX-RZ630 has a power of 90/8, 215/6. The THD is the same and is 0.08%.
Characteristics of digital to analog converter (DAC) are different, Hi-Grade 384 KHz/32-bit for TX-NR555 and AK4458 384 KHz/32-bit for the TX-RZ630. Both the TX-NR555 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.
WI-FI modules have the same characteristics: 2.4/5GHz. Rivals from our review have Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay. Spotify can be used on each receiver. Deezer, TIDAL, Pandora - all of these streaming services have found application in each of the models. 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 Onkyo TX-NR555 has 6/1 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. These compared receivers have a built-in phono stage for connecting a vinyl player.
The TX-NR555 supports 2 Multi-room zones, versus 3 for the TX-RZ630. An ECO mode is only available for the TX-NR555. The setup assistant will help you configure Onkyo TX-RZ630.
Both devices have support for Dolby Atmos multichannel audio format. The surround sound technology DTS:X is supported by devices under review.