An affordable AV receiver is always a good option to consider, so Onkyo TX-NR555 vs Onkyo TX-8140 comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Onkyo TX-NR555 has 7.2 versus 2.0 for Onkyo TX-8140. Regarding power, then TX-NR555 has such a W/Ohm ratio - 130/6 when TX-8140 has a power of 80/8, 110/6. 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 AK4458 384 KHz/32-bit for the TX-8140. 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. Rivals from our review have Bluetooth support. Spotify can be used on each receiver. The TX-NR555 can work with the audio stream from Deezer, TIDAL, Pandora, and the TX-8140 can receive a content from SiriusXM.
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. Only the TX-NR555 supports HDMI Audio Return Channel (ARC). Unfortunately, HDMI eARC is not available on monitored devices. Of the two receivers in our comparison, HDMI CEC is present in only the TX-NR555. These compared receivers have 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. The setup assistant will help you configure Onkyo TX-8140.
Only the TX-NR555 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-NR555.