An affordable AV receiver is always a good option to consider, so Onkyo TX-NR555 vs Sony STR DH550 comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Onkyo TX-NR555 has 7.2 versus 5.2 for Sony STR DH550. Regarding power, then TX-NR555 has such a W/Ohm ratio - 130/6 when STR DH550 has a power of 90/6. The THD is 0.08% for the TX-NR555 but 0.09% for the STR DH550.
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 STR DH550. Only the TX-NR555 supports Bi-amping feature. The Onkyo TX-NR555 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Only the TX-NR555 has Bluetooth support. Only the TX-NR555 supports Spotify.
Only the Onkyo TX-NR555 has support for High dynamic range (HDR). Only the TX-NR555 provides HDMI signal transmission in standby mode. 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 4/1 HDMI connectors of the Sony STR DH550. 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. The TX-NR555 has a built-in phono stage for connecting a vinyl player. A voice control is not available. An ECO mode is only available for the TX-NR555. Unfortunately, the setup assistant is not available in each of the models.
Only the TX-NR555 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-NR555.