Bose Soundlink with itunes

I'd like to send my itunes audio to the external Bose speakers via soundlink while keeping all of the non-itunes audio on my imac internal speakers. The default way of operating soundlink (which is a USB wireless deal) is to switch to external speakers in the control panel which sends ALL the computer audio to the external speakers and turns off the internal imac speakers.

From what I can tell in my searches, it appears that I would at least need airport express to pull of the split audio, and even then I'm not too sure if that would work.

If anyone can set me straight or point me in the right direction I would be much obliged.

Thanks