I don’t think there will be an App for this. You are right the WAM550s can use a “Samsung MultiRoom” App, but the TV cannot. That App is only intended for a series of Speakers that Samsung released a few years ago.
Both can add to the SmartThings App, but I don’t think you could “link” them here in the way you are looking for (turn them both on via Scene or something, sure).
The TV does have a Bluetooth connection, which you could link to at least one Speaker, perhaps both. This might accomplish at least part of what you want done, but I’m not sure. Anyways, hope that is at least somewhat helpful. Let me know if you have more questions!