An affordable AV receiver is always a good option to consider, so Yamaha RX-V585BL vs Onkyo TX-8140 comparison definitely makes sense.
A significant difference between the receivers in the number of channels, Yamaha RX-V585BL has 7.2 versus 2.0 for Onkyo TX-8140. Regarding power, then RX-V585BL has such a W/Ohm ratio - 80/8, 145/6 when TX-8140 has a power of 80/8, 110/6. The THD is 0.09% for the RX-V585BL but 0.08% for the TX-8140.
Characteristics of digital to analog converter (DAC) are different, Burr-Brown 384 KHz/32-bit for RX-V585BL and AK4458 384 KHz/32-bit for the TX-8140. Only the RX-V585BL 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 RX-V585BL can work with the audio stream from Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, and the TX-8140 can receive a content from SiriusXM. Only the RX-V585BL provides HDMI signal transmission in standby mode. The RX-V585BL can scale the input HDMI signal, unlike the TX-8140. Dolby Vision technology found support only on the RX-V585BL. Only the RX-V585BL supports HDMI Audio Return Channel (ARC). The HDMI eARC is available only on the RX-V585BL. Of the two receivers in our comparison, HDMI CEC is present in only the RX-V585BL. The TX-8140 has a built-in phono stage for connecting a vinyl player. An ECO mode is only available for the RX-V585BL. Both RX-V585BL and TX-8140 can be configured using the Setup assistant.
Only the RX-V585BL has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the RX-V585BL.