It makes sense comparing Pioneer VSX-LX303 vs Onkyo TX-RZ630 because they both are able to give some premium features.
Considered AV receivers have the same number of channels 9.2. Regarding power, then VSX-LX303 has such a W/Ohm ratio - 100/8, 200/6 when TX-RZ630 has a power of 90/8, 215/6. The THD is the same and is 0.08%.
Competitors' digital to analog converter (DAC) is identical to AK4458 384 KHz/32-bit. Both the VSX-LX303 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. The VSX-LX303 can work with the audio stream from Deezer, TIDAL, Pandora, TuneIn Radio, and the TX-RZ630 can receive a content from Deezer, TIDAL, Pandora.
Both AV receivers support HDR10 technology (High dynamic range). 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 VSX-LX303 can scale the input HDMI signal, unlike the TX-RZ630. The HDR standard - Dolby Vision is supported by these receivers.
Each receiver has 7/2 HDMI inputs/outputs. 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.
Each of the AV receivers from our review supports 3 Multi-room zones. Supported voice control technologies are identical - Google Assistant. An ECO mode is not present in each of the AV receivers. Both VSX-LX303 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.