I like Hi Five, but how much of their music can I listen to on endless repeat? How many Doctor Who soundtracks can Lex listen to before he starts screaming?

You like Hi Five? I don't think we can be friends anymore ;-)
No, what I wanted to point out was that kids love the familiar, and love repetition. So Dr Who soundtracks should be fine!
I watched so much M*A*S*H and BtVS while I was pregnant that for a short while after she was born Abbey would pay close attention when either of those themes were played.