Split Screens with Audio

Hi - I am using FCPX and downloaded a package of many different kinds of splitscreens (Multi Screen Frame Pack). I want to do a split screen where one side is a “talking head,” and the other side is B-roll. With this (or any other?) frame pack, how can I include the AUDIO to the clip as well? I’d rather not split it and put it as a separate audio track, because I don’t want it slipping off synch…any help appreciated, thanks!