It’s strongly recommended to compare different receivers if you want to choose the best one: Denon AVR-S640H vs Denon AVR-X6500H.
The number of channels for receivers is different - 5.2 versus 11.2, 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 AVR-X6500H has a power of 140/8, 175/6. The value of total harmonic distortion is also different, and for the AVR-S640H it is 0.08%, but for the AVR-X6500H it is 0.05%.
Competitive models use the same DAC. The Bi-amping function is implemented only in the Denon AVR-X6500H. Both Denon AVR-S640H and Denon AVR-X6500H can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
Wireless Internet access via WIFI is possible on both units. 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 Denon AVR-X6500H works with Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, iHeart Radio, Sound Cloud, Mood Mix. The quality of 4K/60Hz signal remains unchanged when transmitting from a source to a TV or projector via HDMI for both receivers. Signaling over HDMI in standby mode can provide the AVR-S640H and the AVR-X6500H. Video scaling is only possible with the AVR-X6500H. 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 AVR-X6500H has 8/3. HDMI Audio Return Channel is implemented in both devices. HDMI eARC is only supported by the AVR-X6500H. When comparing receivers, it becomes clear that each of the rivals can work with HDMI CEC. AVR-S640H and AVR-X6500H support the standard HDCP 2.2. 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 Denon AVR-X6500H can be properly configured using the setup assistant.
A Dolby Atmos multichannel audio format is available only in the AVR-X6500H. Only in the AVR-X6500H realized a DTS:X surround technology.