How can you include sound in motion graphics templates?

How can you make a motion graphic that includes sound, export it as a motion graphics template so it can be used over and over again without having to rebuild it and add a sound track every time you use it? This should be simple but no instructions anywhere to be found, and I've searched and searched online. It is easy to draw put a video in a layer in the edit tab of the motion graphics, but the video has no sound. I've drawn a simple shape, chose "Replace with After effects compsition" and brought in a short video clip, but can't get the sound to play. It doesn't make sense that Adobe would make tools with such limited and amaturish abilities for a program that they tout as Premiere and Professional... I must be missing something. Can anyone point me in the right direction?