It makes sense comparing Onkyo PR-RZ5100 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 PR-RZ5100 has 11.2 versus 2.0 for Onkyo TX-8020. The THD is 0.06% for the PR-RZ5100 but 0.03% for the TX-8020.
Characteristics of digital to analog converter (DAC) are different, AKM 384 KHz/32-bit for PR-RZ5100 and 192 KHz/24-bit for the TX-8020. Only the PR-RZ5100 supports Bi-amping feature. The Onkyo TX-8020 can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
Only the Onkyo PR-RZ5100 can connect to the Internet via WI-FI. Only the PR-RZ5100 has Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay. Only the PR-RZ5100 supports Spotify. Only the PR-RZ5100 provides HDMI signal transmission in standby mode. The PR-RZ5100 can scale the input HDMI signal, unlike the TX-8020. Dolby Vision technology found support only on the PR-RZ5100. Only the PR-RZ5100 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 PR-RZ5100. These compared receivers have a built-in phono stage for connecting a vinyl player. A voice control is not available. An ECO mode is not present in each of the AV receivers. The setup assistant will help you configure Onkyo PR-RZ5100.
Only the PR-RZ5100 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the PR-RZ5100.