Sadly the PS3 can only use music stored on the internal hd (external ones don't count -_-') during games. For some games it's even limited to mp3 only, and no aac. I was pretty deluded about that, as for me music in game meant "streamed off my Mac" as i did with Connect360 and my Xbox.
So.... nothing to do, and MediaLink is fairly inferior to PS3 Media Server
