An affordable AV receiver is always a good option to consider, so Onkyo TX-NR575 vs Onkyo TX-8140 comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Onkyo TX-NR575 has 7.2 versus 2.0 for Onkyo TX-8140. Regarding power, then TX-NR575 has such a W/Ohm ratio - 135/6 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, 384 KHz/32-bit for TX-NR575 and AK4458 384 KHz/32-bit for the TX-8140. Only the TX-NR575 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-NR575 can work with the audio stream from Deezer, TIDAL, Pandora, TuneIn Radio, and the TX-8140 can receive a content from SiriusXM. Only the TX-NR575 provides HDMI signal transmission in standby mode. Both competitors are not able to scale the HDMI signal. Dolby Vision technology found support only on the TX-NR575. Only the TX-NR575 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-NR575. These compared receivers have a built-in phono stage for connecting a vinyl player. A voice control is not available. An ECO mode is not present in each of the AV receivers. Both TX-NR575 and TX-8140 can be configured using the Setup assistant.
Only the TX-NR575 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-NR575.