An affordable AV receiver is always a good option to consider, so Yamaha RX-V685BL vs Onkyo TX-8140 comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Yamaha RX-V685BL has 7.2 versus 2.0 for Onkyo TX-8140. Regarding power, then RX-V685BL has such a W/Ohm ratio - 90/8, 150/4 when TX-8140 has a power of 80/8, 110/6. The THD is 0.06% for the RX-V685BL but 0.08% for the TX-8140.
Characteristics of digital to analog converter (DAC) are different, Burr-Brown 384 KHz/32-bit for RX-V685BL and AK4458 384 KHz/32-bit for the TX-8140. Only the RX-V685BL 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. Only the TX-8140 supports Spotify. Only the RX-V685BL provides HDMI signal transmission in standby mode. The RX-V685BL can scale the input HDMI signal, unlike the TX-8140. Dolby Vision technology found support only on the RX-V685BL. Only the RX-V685BL supports HDMI Audio Return Channel (ARC). The HDMI eARC is available only on the RX-V685BL. Of the two receivers in our comparison, HDMI CEC is present in only the RX-V685BL. 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 RX-V685BL. Both RX-V685BL and TX-8140 can be configured using the Setup assistant.
Only the RX-V685BL has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the RX-V685BL.