It makes sense comparing Onkyo TX-RZ820 vs Onkyo TX-8020 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Onkyo TX-RZ820 has 7.2 versus 2.0 for Onkyo TX-8020. Regarding power, then TX-RZ820 has such a W/Ohm ratio - 160/8 when TX-8020 has a power of 90/6. The THD is 0.08% for the TX-RZ820 but 0.03% for the TX-8020.
Characteristics of digital to analog converter (DAC) are different, AK4458 384 KHz/32-bit for TX-RZ820 and 192 KHz/24-bit for the TX-8020. Only the TX-RZ820 supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Only the TX-RZ820 has Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay. Only the TX-RZ820 supports Spotify. Only the TX-RZ820 provides HDMI signal transmission in standby mode. Both competitors are not able to scale the HDMI signal. Dolby Vision technology found support only on the TX-RZ820. Only the TX-RZ820 supports HDMI Audio Return Channel (ARC). Unfortunately, HDMI eARC is not available on monitored devices. Of the two receivers in our comparison, HDMI CEC is present in only the TX-RZ820. These compared receivers have a built-in phono stage for connecting a vinyl player. A voice control is not available. An ECO mode is only available for the TX-RZ820. The setup assistant will help you configure Onkyo TX-RZ820.
Only the TX-RZ820 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-RZ820.