Thanks for your question! As the TV only runs one app at a time, I don't be believe it's currently possible for the apps to run over top the others, so that there would be sound from one app in the background and an image from another app in the foreground.
Just recently purchased a 5500 series Smart TV which I hooked up to the speaker system that covers the whole house. My plan was to listen to various radio stations (using the TuneIn app) through my TV but I noticed that there is no "screensaver" that kicks-in after a short period of time. I'm afraid I might get screen burn! I contacted Samsung and apparently they don't have "screensavers" for their TV's. Are there apps that I can download to take care of this?