It makes sense comparing Denon AVR-S660H vs Yamaha RX-V485 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Denon AVR-S660H has 5.2 versus 5.1 for Yamaha RX-V485. Regarding power, then AVR-S660H has such a W/Ohm ratio - 75/8, 100/6 when RX-V485 has a power of 80/8, 145/6. The THD is 0.08% for the AVR-S660H but 0.09% for the RX-V485.
Characteristics of digital to analog converter (DAC) are different, 192 KHz/32-bit for AVR-S660H and Burr-Brown 384 KHz/32-bit for the RX-V485. Only the RX-V485 supports Bi-amping feature. The Yamaha RX-V485 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Rivals from our review have Bluetooth support. The Apple Music service is implemented on considered devices: AirPlay, AirPlay 2. Spotify can be used on each receiver. The AVR-S660H can work with the audio stream from Deezer, TIDAL, Pandora, SiriusXM, Napster, SoundCloud, and the RX-V485 can receive a content from Deezer, TIDAL, Pandora, Napster, SiriusXM.
HDMI signal transmission in standby mode is implemented in each of the devices. Both rivals can scale the resolution of the incoming HDMI signal. The HDR standard - Dolby Vision is supported by these receivers.
The Denon AVR-S660H has 6/1 HDMI inputs/outputs versus 4/1 HDMI connectors of the Yamaha RX-V485. The HDMI Audio Return Channel (ARC) feature supports both devices. HDMI eARC is available in each model. 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 2.3. The AVR-S660H has a built-in phono stage for connecting a vinyl player. The AVR-S660H supports voice control via Amazon Alexa, Google Assistant, Siri, Josh.AI, and the RX-V485 - Amazon Alexa, Google Assistant, Siri. It is also worth noting that the ECO mode is presented in each of the receivers. Both AVR-S660H and RX-V485 can be configured using the Setup assistant.
Only the AVR-S660H has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the AVR-S660H.