Using an Mbox with Soundtrack Pro - How to set up?

I'm trying to monitor my Soundtrack projects through my Mbox, just as I do in Final Cut, but can't find a comparable pulldown menu that lets me select for this. There are pulldowns in the recording window that let me connect a microphone through the Mbox, but I can't find any project preferences that tell Soundtrack to use a USB device for audio interface. I'm using Soundtrack 2.0 on a PPC G5.