The hardware support for Siri on Denon speakers, first reported on by HomeKit News, came with the U32 firmware update released in December. It allows you to talk to Apple’s assistant through the speakers to control music playback, initiate smart home commands through Apple Home, or do most of anything you are used to using Siri for. Unlike using Siri on an Ecobee Thermostat, the audio quality should be a lot better on a Denon speaker than the thermostat on your wall.
Models with the capability include the Denon Home series 150, 250, 350, and Soundbar 550, which start at $250. These all offer Amazon Alexa voice assistant integration and Apple AirPlay 2 support, too, but as with the Ecobee thermostat, you can’t have both Siri and Alexa running simultaneously; you need to choose one or the other. And, as Siri is not built into the device, you also need to have a HomePod or HomePod Mini on the same Wi-Fi network to process the commands. Denon has instructions for activating the new Siri feature on its site.