I haven’t changed the current volume stuff. Your volume intents specified in the Advanced settings still work.
If you have two HD Radio buttons, one on the side and one on the homescreen, you can have both of them fire the intent to change the input.
For example, in Settings/IO Config/Actions you could set the global HD Radio button to change the input. Click Global Buttons/HD Radio/System/Broadcast Intent. A dialog will popup, fill in the intent on the left, and the channel data on the right under Extra Data, just like before. Click save. Now both HD Radio buttons will send the intent to change the input.
If you click home and then click the button again, the intent will still be broadcast a second time, but since you’re already on that input you shouldn’t see any change.
Following the same procedure, you can have another button to change to built in radio, or internal music or whatever other inputs you have.