It makes sense comparing Onkyo TX-NR555 vs Marantz NR1509 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Onkyo TX-NR555 has 7.2 versus 5.2 for Marantz NR1509. Regarding power, then TX-NR555 has such a W/Ohm ratio - 130/6 when NR1509 has a power of 50/8, 60/6. 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 192 KHz/24-bit for the NR1509. Only the TX-NR555 supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
WI-FI modules have the same characteristics: 2.4/5GHz. 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 NR1509 can receive a content from Deezer, Pandora, 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. Dolby Vision technology found support only on the NR1509.
The Onkyo TX-NR555 has 6/1 HDMI inputs/outputs versus 7/1 HDMI connectors of the Marantz NR1509. 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. It is also worth noting that the ECO mode is presented in each of the receivers. The setup assistant will help you configure Marantz NR1509.
Only the TX-NR555 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-NR555.