An affordable AV receiver is always a good option to consider, so Pioneer VSX-S520 vs Onkyo TX-8140 comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Pioneer VSX-S520 has 5.1 versus 2.0 for Onkyo TX-8140. Regarding power, then VSX-S520 has such a W/Ohm ratio - 50/4 when TX-8140 has a power of 80/8, 110/6. The THD is 0.09% for the VSX-S520 but 0.08% for the TX-8140.
Characteristics of digital to analog converter (DAC) are different, 192 KHz/24-bit for VSX-S520 and AK4458 384 KHz/32-bit for the TX-8140. None of the models 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. Spotify can be used on each receiver. The VSX-S520 can work with the audio stream from Deezer, TIDAL, TuneIn Radio, and the TX-8140 can receive a content from SiriusXM.
Only the Pioneer VSX-S520 has support for High dynamic range (HDR). Only the VSX-S520 provides HDMI signal transmission in standby mode. The VSX-S520 can scale the input HDMI signal, unlike the TX-8140. Dolby Vision technology found support only on the VSX-S520. Only the VSX-S520 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 VSX-S520. 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 VSX-S520 and TX-8140 can be configured using the Setup assistant.
Only the VSX-S520 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the VSX-S520.