What (Apple TV, PS5, Cable Box) are connected to it?

To help determine the best next step for your specific setup, please let me know:

If your unit has never been updated, you can try to trigger an update, although the AVR-591 does not have built-in Wi-Fi or Ethernet connectivity to check for updates over the internet like modern Denon units. Method 1: USB Firmware Update (Most Likely Method)

If you have HDMI compatibility issues, use a modern HDMI 2.1 switch or an HDFury device to handle the handshake before the signal reaches the Denon.

: Official firmware patches for this model are typically intended for authorized service centers. These updates are used to address specific hardware-level bugs, such as HDMI handshake issues or signal processing errors.

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Do not turn off the power during the update process. A power loss during an update can permanently damage the unit.

On the remote, press > General > Firmware (if available in your specific regional menu).

to see if a hardware-level update is available for your unit?

: Complete audio dropouts during Dolby Digital or DTS playback.

[4K Source Device] ───(HDMI Cable)───> [4K Smart TV] │ (Optical Audio Cable) │ ▼ [Denon AVR-591]

: Fixing issues where surround sound detection fails or specific channels drop out.

: Requires a physical connection via the receiver's internal service port.

The Denon AVR-591 firmware update patched has addressed several key issues and added new features to this popular home theater receiver. By keeping your device up to date, you can ensure that you're enjoying the best possible performance and features. If you're experiencing issues with your AVR-591 or want to take advantage of the latest features, we highly recommend updating your firmware.