It makes sense comparing Yamaha RX-V581 vs Yamaha RX-V671 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Yamaha RX-V581 has 7.2 versus 7.1 for Yamaha RX-V671. Regarding power, then RX-V581 has such a W/Ohm ratio - 115/6 when RX-V671 has a power of 90/8, 150/4. The THD is the same and is 0.09%.
Competitors' digital to analog converter (DAC) is identical to Burr-Brown 192 KHz/24-bit. Both the RX-V581 and the RX-V671 support Bi-amping. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
Only the Yamaha RX-V581 can connect to the Internet via WI-FI. Rivals from our review have Bluetooth support. Only the RX-V581 supports Spotify. The RX-V581 can work with the audio stream from Pandora, JUKE, and the RX-V671 can receive a content from Napster.
Only the Yamaha RX-V581 has support for High dynamic range (HDR). Compared AV receivers retain the quality of 4K/60Hz signal when transmitting from a source to a TV or projector. HDMI signal transmission in standby mode is implemented in each of the devices. The RX-V671 can scale the input HDMI signal, unlike the RX-V581. The HDR standard - Dolby Vision is not supported by these receivers.
The Yamaha RX-V581 has 4/1 HDMI inputs/outputs versus 6/1 HDMI connectors of the Yamaha RX-V671. The HDMI Audio Return Channel (ARC) feature supports both devices. Unfortunately, HDMI eARC is not available on monitored devices. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. Both models support the standard HDCP 2.2. The RX-V671 has a built-in phono stage for connecting a vinyl player.
Each of the AV receivers from our review supports 2 Multi-room zones. A voice control is not available. An ECO mode is only available for the RX-V581. The setup assistant will help you configure Yamaha RX-V581.
Only the RX-V581 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the RX-V581.