Having had an opportunity to test Denon AVR-S640H vs Onkyo TX-NR7100, I’d like to share my impression here to facilitate your choice of a new AV receiver.
The number of channels for receivers is different - 5.2 versus 9.2, respectively, for devices. In terms of power, there are differences, the AVR-S640H has such a ratio W/Ohm - 75/8, 100/6, while the TX-NR7100 has a power of 100/8, 220/6. A common feature for devices is the same total harmonic distortion - 0.08%.
The manufacturer installed different DACs, the AVR-S640H received the model 192 KHz/32-bit, but the TX-NR7100 is equipped with 384 KHz/32-bit. The Bi-amping function is implemented only in the Onkyo TX-NR7100. Both Denon AVR-S640H and Onkyo TX-NR7100 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Each of the receivers has a Bluetooth connector. Both devices can work with such Apple Music services: AirPlay, AirPlay 2. Access to the Spotify service is on each of the competitors. The number of available streaming services varies for receivers, the Denon AVR-S640H works with Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, iHeart Radio, Sound Cloud, but the Onkyo TX-NR7100 works with Deezer, TIDAL, Pandora, SiriusXM, Napster, SoundCloud. Signaling over HDMI in standby mode can provide the AVR-S640H and the TX-NR7100. Video scaling is only possible with the TX-NR7100. Each of the participants of the comparison has a Dolby Vision.
The number of HDMI inputs/outputs varies depending on the receiver, the AVR-S640H has 5/1, and the TX-NR7100 has 7/2. HDMI Audio Return Channel is implemented in both devices. HDMI eARC is only supported by the TX-NR7100. When comparing receivers, it becomes clear that each of the rivals can work with HDMI CEC. The AVR-S640H has support for the standard HDCP 2.2, compared to the TX-NR7100, which supports the standard HDCP 2.3. Like most receivers, our models have a built-in phono stage for connecting a vinyl player. Voice control is performed using Amazon Alexa, Google Assistant, Siri, Josh.AI in both models. There is an ECO mode in either AV receiver. The Denon AVR-S640H and the Onkyo TX-NR7100 can be properly configured using the setup assistant.
A Dolby Atmos multichannel audio format is available only in the TX-NR7100. Only in the TX-NR7100 realized a DTS:X surround technology.