Having had an opportunity to test Onkyo TX-NR646 vs Onkyo TX-NR545, I’d like to share my impression here to facilitate your choice of a new AV receiver.
AV receivers under review have the same number of channels. In terms of power, there are differences, the TX-NR646 has such a ratio W/Ohm - 160/6, while the TX-NR545 has a power of 100/6. A common feature for devices is the same total harmonic distortion - 0.08%.
Competitive models use the same DAC. Each of the compared opponents supports Bi-amping. Both Onkyo TX-NR646 and Onkyo TX-NR545 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. Access to the Spotify service is on each of the competitors. The number of available streaming services varies for receivers, the Onkyo TX-NR646 works with Deezer, TuneIn Radio, but the Onkyo TX-NR545 works with Tunein Radio.
Support for the HDR function can only boast of each of the AV receivers. 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 TX-NR646 and the TX-NR545. None of the devices can increase the resolution of the incoming video signal. Review participants do not have the Dolby Vision feature.
The number of HDMI inputs/outputs varies depending on the receiver, the TX-NR646 has 8/2, and the TX-NR545 has 6/1. HDMI Audio Return Channel is implemented in both devices. HDMI eARC is not supported by the TX-NR646 and the TX-NR545. When comparing receivers, it becomes clear that each of the rivals can work with HDMI CEC. TX-NR646 and TX-NR545 support the standard HDCP 2.2. In the presence of a built-in phono stage for connecting a vinyl player only at Onkyo TX-NR646.
Ability to create 2 Multi zones inherent in both AV receivers. Voice control of the basic functions of the receiver is not realized in both models. There is an ECO mode in TX-NR646. The Onkyo TX-NR646 and the Onkyo TX-NR545 can be properly configured using the setup assistant.
A Dolby Atmos multichannel audio format is available both models. Only in the TX-NR646 realized a DTS:X surround technology.