Problems interface connection in Garageband

I've been using a Lexicon Alpha interface with Garageband for a long time. A few days ago a problem occured. Whenever I play my Garageband project through the interface, nothing comes out but a brutally distorted noise. The instruments connected to the interface still sound normal. So there's nothing wrong with the direct sound, but the playback is messed up. While trying to solve the problem I tried a few combinations in the Audio/MIDI settings, and found out that when I set the Audio in to built-in microphone and Audio out to the Lexicon Alpha, playback works. Of course this does not solve the problem since I want to be able to record with my interface while playing back through it.

Any tips on what I could do?