Alright, what I’ve got right now. You can add custom intents to ANY button. So in your case, create or edit your “HD Tuner” button. In the new “Custom Intent” field, add your intent to change source. Now as soon as you press the HD Tuner button on the home screen that intent will fire. There is no error checking for if it’s valid or not, because ANYTHING could be a valid intent.
Now you’ll stay on the HD Tuner input. To get back, add another custom intent, but this time to the music button. Use this one to change back to your internal audio source. Add the same intent for anything that needs internal audio such as another media player.
I’ll push this to latest nightly so you can try it out if you’d like.