It makes sense comparing Denon AVR-X3500H 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, Denon AVR-X3500H has 7.2 versus 2.0 for Onkyo TX-8020. Regarding power, then AVR-X3500H has such a W/Ohm ratio - 105/8, 135/6 when TX-8020 has a power of 90/6. The THD is 0.05% for the AVR-X3500H but 0.03% for the TX-8020.
Characteristics of digital to analog converter (DAC) are different, AKM 192 KHz/32-bit for AVR-X3500H and 192 KHz/24-bit for the TX-8020. Only the AVR-X3500H 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 AVR-X3500H has Bluetooth support. The Denon AVR-X3500H has support for AirPlay, AirPlay 2, and its competitor in our comparison - AirPlay. Only the AVR-X3500H supports Spotify. Only the AVR-X3500H provides HDMI signal transmission in standby mode. The AVR-X3500H can scale the input HDMI signal, unlike the TX-8020. Dolby Vision technology found support only on the AVR-X3500H. Only the AVR-X3500H 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 AVR-X3500H. These compared receivers have a built-in phono stage for connecting a vinyl player. An ECO mode is only available for the AVR-X3500H. The setup assistant will help you configure Denon AVR-X3500H.
Only the AVR-X3500H has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the AVR-X3500H.
The Denon AVR-X3500H is better receiver in this comparison. Check Denon AVR-X3500H price