It makes sense comparing Onkyo TX-NR555 vs Onkyo TX-NR595 because they both are able to give some premium 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-NR595 has a power of 80/8, 170/6. The THD is the same and is 0.08%.
Characteristics of digital to analog converter (DAC) are different, Hi-Grade 384 KHz/32-bit for TX-NR555 and AKM 384 KHz/32-bit for the TX-NR595. Both the TX-NR555 and the TX-NR595 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 Onkyo TX-NR555 has support for AirPlay, and its competitor in our comparison - AirPlay, AirPlay 2. Spotify can be used on each receiver. The TX-NR555 can work with the audio stream from Deezer, TIDAL, Pandora, and the TX-NR595 can receive a content from Deezer, TIDAL, Pandora, TuneIn Radio. 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 TX-NR595 can scale the input HDMI signal, unlike the TX-NR555. Dolby Vision technology found support only on the TX-NR595.
The Onkyo TX-NR555 has 6/1 HDMI inputs/outputs versus 6/2 HDMI connectors of the Onkyo TX-NR595. 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. An ECO mode is only available for the TX-NR555. The setup assistant will help you configure Onkyo TX-NR595.
Both devices have support for Dolby Atmos multichannel audio format. The surround sound technology DTS:X is supported by devices under review.