Onkyo TX-NR555 vs Yamaha RX-V681BL comparison definitely makes sense.
Considered AV receivers have the same number of channels 7.2. Regarding power, then TX-NR555 has such a W/Ohm ratio - 130/6 when RX-V681BL has a power of 90/8, 150/4. The THD is 0.08% for the TX-NR555 but 0.06% for the RX-V681BL.
Characteristics of digital to analog converter (DAC) are different, Hi-Grade 384 KHz/32-bit for TX-NR555 and Burr-Brown 192 KHz/24-bit for the RX-V681BL. Both the TX-NR555 and the RX-V681BL support Bi-amping. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Rivals from our review have Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay. Spotify can be used on each receiver. The TX-NR555 can work with the audio stream from Deezer, TIDAL, Pandora, and the RX-V681BL can receive a content from Pandora, Sirius XM, Napster, JUKE, Qobuz. Compared AV receivers retain the quality of 4K/60Hz signal when transmitting from a source to a TV or projector. HDMI signal transmission in standby mode is implemented in each of the devices. The RX-V681BL can scale the input HDMI signal, unlike the TX-NR555. Dolby Vision technology found support only on the RX-V681BL.
Each receiver has 6/1 HDMI inputs/outputs. The HDMI Audio Return Channel (ARC) feature supports both devices. Unfortunately, HDMI eARC is not available on monitored devices. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. Both models support the standard HDCP 2.2. These compared receivers have a built-in phono stage for connecting a vinyl player.
Each of the AV receivers from our review supports 2 Multi-room zones. A voice control is not available. It is also worth noting that the ECO mode is presented in each of the receivers. The setup assistant will help you configure Yamaha RX-V681BL.
Both devices have support for Dolby Atmos multichannel audio format. The surround sound technology DTS:X is supported by devices under review.