It makes sense comparing Yamaha RX-V685BL 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-V685BL has 7.2 versus 7.1 for Yamaha RX-V671. And as for power, it is the same and equal to 90/8, 150/4. The THD is 0.06% for the RX-V685BL but 0.09% for the RX-V671.
Characteristics of digital to analog converter (DAC) are different, Burr-Brown 384 KHz/32-bit for RX-V685BL and Burr-Brown 192 KHz/24-bit for the RX-V671. Both the RX-V685BL 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. Rivals from our review have Bluetooth support. Competitors do not have built-in Spotify service. 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. Both rivals can scale the resolution of the incoming HDMI signal. Dolby Vision technology found support only on the RX-V685BL.
The Yamaha RX-V685BL has 5/2 HDMI inputs/outputs versus 6/1 HDMI connectors of the Yamaha RX-V671. The HDMI Audio Return Channel (ARC) feature supports both devices. The HDMI eARC is available only on the RX-V685BL. 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. These compared receivers have 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-V685BL. The setup assistant will help you configure Yamaha RX-V685BL.
Only the RX-V685BL has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the RX-V685BL.