I've installed Saffire on my Mac, but audio playback still comes out my mac's internal speakers. How do I route audio to the Saffire instead?

Open the Mac AudioMIDISetup utility located in Applications/Utilities. Once the AudioMIDISetup Control Panel appears, you will see several soundcard options including Default Output, and System Output.Change these options from Built-In Audio to Saffire. System Output routes system sounds such as alerts, while Default Output routes audio out of CoreAudio applications.