Having had an opportunity to test Onkyo TX-SR353 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 TX-SR353 has such a ratio W/Ohm - 140/6, while the AVR-X3700H has a power of 105/8, 135/6. A common feature for devices is the same total harmonic distortion - 0.08%. The Bi-amping function is implemented only in the Denon AVR-X3700H. The model AVR-X3700H can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Each of the receivers has a Bluetooth connector. The AVR-X3700H has access to the Spotify service. Signaling over HDMI in standby mode can provide the TX-SR353 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 TX-SR353 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 TX-SR353 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. 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.