Both Rasplex (OpenPHT) and the official Plex distro for pi are now based on LE, we've been working together .. but LE assumes that there is only one mediacentre application running full-screen. In theory you could combine both apps into one image, but even if you did they would run discretely and you'd need to figure out the window management. You don't just add LiveTV to Plex or transcoding to Kodi - serious coding work is required.
NB: The rule for these things; if you need to ask how it's done you won't succeed. If you have the skills to succeed, our buildsystem already made sense to you and you're compiling something. It's a very arrogant statement (sorry) but experience also shows it's true.