It makes sense comparing Yamaha TSR-5810 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, Yamaha TSR-5810 has 7.2 versus 2.0 for Onkyo TX-8020. Regarding power, then TSR-5810 has such a W/Ohm ratio - 80/8, 145/6 when TX-8020 has a power of 90/6. The THD is 0.09% for the TSR-5810 but 0.03% for the TX-8020.
Characteristics of digital to analog converter (DAC) are different, Burr-Brown 192 KHz/24-bit for TSR-5810 and 192 KHz/24-bit for the TX-8020. Only the TSR-5810 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 Yamaha TSR-5810 can connect to the Internet via WI-FI. Only the TSR-5810 has Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay. Only the TSR-5810 supports Spotify.
Only the Yamaha TSR-5810 has support for High dynamic range (HDR). Only the TSR-5810 provides HDMI signal transmission in standby mode. Both competitors are not able to scale the HDMI signal. The HDR standard - Dolby Vision is not supported by these receivers. Only the TSR-5810 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 TSR-5810. The TX-8020 has a built-in phono stage for connecting a vinyl player. An ECO mode is only available for the TSR-5810. The setup assistant will help you configure Yamaha TSR-5810.
Only the TSR-5810 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TSR-5810.