It makes sense comparing Pioneer VSX-S520 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, Pioneer VSX-S520 has 5.1 versus 2.0 for Onkyo TX-8020. Regarding power, then VSX-S520 has such a W/Ohm ratio - 50/4 when TX-8020 has a power of 90/6. The THD is 0.09% for the VSX-S520 but 0.03% for the TX-8020.
Competitors' digital to analog converter (DAC) is identical to 192 KHz/24-bit. None of the models support Bi-amping. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Only the VSX-S520 has Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay. Only the VSX-S520 supports Spotify.
Only the Pioneer VSX-S520 has support for High dynamic range (HDR). Only the VSX-S520 provides HDMI signal transmission in standby mode. The VSX-S520 can scale the input HDMI signal, unlike the TX-8020. Dolby Vision technology found support only on the VSX-S520. Only the VSX-S520 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 VSX-S520. 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 Pioneer VSX-S520.
Only the VSX-S520 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the VSX-S520.