The Onkyo TX-NR555 vs Onkyo TX-NR646 comparison proves that these receivers have many common features.
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 TX-NR646 has a power of 160/6. The THD is the same and is 0.08%.
Competitors' digital to analog converter (DAC) is identical to Hi-Grade 384 KHz/32-bit. Both the TX-NR555 and the TX-NR646 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 TX-NR646 can receive a content from Deezer, TuneIn Radio.
These units support HDR technology. 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. Both competitors are not able to scale the HDMI signal. The HDR standard - Dolby Vision is not supported by these receivers.
The Onkyo TX-NR555 has 6/1 HDMI inputs/outputs versus 8/2 HDMI connectors of the Onkyo TX-NR646. 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 Onkyo TX-NR646.
Both devices have support for Dolby Atmos multichannel audio format. The surround sound technology DTS:X is supported by devices under review.