Siri

Known Siri commands that work with a Set-Top Box accessory are:

You can control the set-top box by using the name:

• "Hey Siri, turn on SetTopBoxName": turns on the set-top box
• "Hey Siri, turn off SetTopBoxName": turns off the set-top box
• "Hey Siri, start SetTopBoxName": turns on the set-top box
• "Hey Siri, stop SetTopBoxName": turns off the set-top box
• "Hey Siri, pause SetTopBoxName": Siri says "Sorry, I couldn't find that speaker" and does nothing

As you can see, the commands are limited to power on and off. Unfortunately, this is an Apple limitation.

Hopefully Apple will improve Siri control in the future. If you find any more commands, let me know!

Workarounds

Luckily, there are ways of overcoming Apple's Siri limitations for Television channel control. For the methods shown below, you must create a shortcut or a scene for each channel. Depending on how many channels you watch, this may be a few or it may be a lot.

Shortcuts

1. Use the Shortcuts app and create a shortcut for the desired channel (switching the set-top box on and setting the channel accordingly). You can of course add anything else to the shortcut: turn down lights, turn on stereo, close the blinds, etc.
2. Name the shortcut with the desired channel name, example "CNN".
3. Then you can say "Hey Siri ChannelName" and Siri will execute the shortcut with that name, example "Hey Siri CNN".

You could also create a shortcut which brings up a menu and allows you to select a channel by voice command. Then you just have one shortcut to maintain.

Scenes

1. Create a scene containing the configuration of the set-top box (power and input) and any other items (stereo, lights, blinds).
2. Name the scene with the desired name, example "BBC".
3. Then you can say "Hey Siri Set SceneName" and Siri will turn on the respective scene, example "Hey Siri Set BBC". I have found it much more reliable to use "Set" before the scene name, as this prevents Siri being confused by apps with same or similar names.

You may find that Scenes may provide you with more natural language control than a shortcut.