Maybe I am missing something, but I don't see how you can put a duplex receptacle and 12 low voltage connectors in a double gang junction box. The duplex receptacle takes up one side. That means 12 connectors on the other side. I don't remember seeing a commercial plate that will do that. I think you should bit the bullet and install an appropriate size j-box. It isn't very difficult.
BTW there needs to be an approved divider between the high voltage side of the box and the low voltage side in most jurisdictions. Consult your local electrical code.