They didn't. For starters you cannot force someone to go bankrupt, companies go bankrupt of their own accord, because nobody wants to by their products. Second of all, Casady & Greene did not own SoundJam or the code for it, so Apple could not possibly have taken it from them.
They sneakily bought the rights from them by telling C&G that if they didn't sell SoundJam to them, they would destroy their business by creating their own software to compete against it. Not exactly robbing them of their code, but not exactly ethical either. What would we say if Apple suddenly done the same to Blitz Research?