In wall volume control?

Has anyone come across an in-wall volume control (or any volume control, I guess) for an external set of speakers that will work with ST? I have a set of speakers on my patio that are driven by an amplifier in my entertainment center. There’s an in-wall volume control near the patio door that we use to increase or decrease the volume. I’d love to be able to control this from my phone, or from Alexa if we brought the Echo outside. I’ve searched a little bit but haven’t been able to find anything. If there’s nothing available, would it be possible to rig something up using a dimmer?

IFollowing. I’m very interested because I have a whole house audio system. Currently I control it by putting the amps on Aeon smart switches and the receiver controlled by harmony. It works, but it’s not optimal.