It makes sense comparing Yamaha RX-S602 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 RX-S602 has 5.1 versus 2.0 for Onkyo TX-8020. Regarding power, then RX-S602 has such a W/Ohm ratio - 80/8, 125/6 when TX-8020 has a power of 90/6. The THD is 0.08% for the RX-S602 but 0.03% for the TX-8020.
Characteristics of digital to analog converter (DAC) are different, Burr-Brown 384 KHz/32-bit for RX-S602 and 192 KHz/24-bit for the TX-8020. Only the RX-S602 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 RX-S602 has Bluetooth support. The Yamaha RX-S602 has support for AirPlay, AirPlay 2, and its competitor in our comparison - AirPlay. Only the RX-S602 supports Spotify. Only the RX-S602 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 RX-S602 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 RX-S602. The TX-8020 has a built-in phono stage for connecting a vinyl player. An ECO mode is only available for the RX-S602. The setup assistant will help you configure Yamaha RX-S602.
None of the rivals equipped with Dolby Atmos multichannel audio decoder. The receivers do not support the surround sound technology DTS:X.