Having had an opportunity to test Denon HEOS AVR vs Denon AVR-X3700H, 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 - 5.1 versus 9.2, respectively, for devices. In terms of power, there are differences, the HEOS AVR has such a ratio W/Ohm - 50/8, 65/6, while the AVR-X3700H has a power of 105/8, 135/6. The value of total harmonic distortion is also different, and for the HEOS AVR it is 0.05%, but for the AVR-X3700H it is 0.08%. The Bi-amping function is implemented only in the Denon AVR-X3700H. Both Denon HEOS AVR and Denon AVR-X3700H can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Each of the receivers has a Bluetooth connector. Access to the Spotify service is on each of the competitors. The number of available streaming services varies for receivers, the Denon HEOS AVR works with Deezer, TIDAL, Pandora, Napster, SiriusXM, TuneIn Radio, iHeart Radio, Sound Cloud, but the Denon AVR-X3700H works with Deezer, TIDAL, Pandora, SiriusXM, Qobuz, TuneIn Radio. Signaling over HDMI in standby mode can provide the HEOS AVR and the AVR-X3700H. Video scaling is only possible with the AVR-X3700H. Operation with the Dolby Vision is only possible with the AVR-X3700H.
The number of HDMI inputs/outputs varies depending on the receiver, the HEOS AVR has 4/1, and the AVR-X3700H has 7/3. HDMI Audio Return Channel is implemented in both devices. HDMI eARC is only supported by the AVR-X3700H. When comparing receivers, it becomes clear that each of the rivals can work with HDMI CEC. The HEOS AVR has support for the standard HDCP 2.2, compared to the AVR-X3700H, which supports the standard HDCP 2.3. In the presence of a built-in phono stage for connecting a vinyl player only at Denon AVR-X3700H. For voice control in the HEOS AVR is used Amazon Alexa, Google Assistant, but in the AVR-X3700H is used Amazon Alexa, Google Assistant, Siri, Josh.AI. There is an ECO mode in AVR-X3700H. The Denon AVR-X3700H can be properly configured using the setup assistant.
A Dolby Atmos multichannel audio format is available only in the AVR-X3700H. Only in the AVR-X3700H realized a DTS:X surround technology.