It makes sense comparing Onkyo TX-SR383 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-SR383 has 7.2 versus 9.2 for Onkyo TX-RZ630. Regarding power, then TX-SR383 has such a W/Ohm ratio - 100/8, 135/6 when TX-RZ630 has a power of 90/8, 215/6. The THD is 0.09% for the TX-SR383 but 0.08% for the TX-RZ630.
Characteristics of digital to analog converter (DAC) are different, 192 KHz/24-bit for TX-SR383 and AK4458 384 KHz/32-bit for the TX-RZ630. Only the TX-RZ630 supports Bi-amping feature. The Onkyo TX-RZ630 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Rivals from our review have Bluetooth support. Only the TX-RZ630 supports Spotify. 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-SR383 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 TX-SR383 supports 2 Multi-room zones, versus 3 for the TX-RZ630. 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.