No audio output?

This is probably an stupid question, but I'm stuck so I'll have to ask it anyway. Just upgraded to Logic 7 from Garageband. Using a Tascam US-122 audio interface into my PowerMac G4 (10.3.9). Opened on of my Garageband projects in Logic 7, and it played just fine. In Garageband, for "real instrument" tracks (ie. those coming through my US-122 in my case), you can monitor(hear) the instrument being played (keyboard, guitar, whatever) in Garageband. When I click on such a "real instrument" track from that project in Logic 7, I hear nothing. At least in terms of MIDI, the US-122 seems to be working, as I can play & hear software instruments via MIDI events from my external keyboard (coming through the US-122). So MIDI events are getting to Logic through the US-122, but either audio is not, or I''ve somehow not setup Logic properly. I've already setup everything through the "Audio MIDI setup" system utility. I've been using the US-122 with Garageband for some time without any issues. Would appreciate any help as this is driving me crazy!!