Put Mission Control to the up-left corner (as Hot Corner) Then, through mission control you can take a a window, and put it between two existing spaces, and app go fullscreen. Then, you can take an other app, and put it inside the fullscreen app, so you take split view.
+ I can't understand why you can't use Safari and itunes. But I can! Actually all my apps can go split view. You have enable 'Display have separate Spaces' at Mission Control, right?
(a quick shot, just to show you that it can happen, and yes Safari+itunes too)
for me, it just work great with every app.