How can you connect your Presonus Firestudio to Garageband or Logic?

Instal the Mac CoreAudio drivers from the CD that came with the Presonus, or better yet, download the latest drivers from Presonus directly. Inside GarageBand, go to Preferences, and choose the Firestudio for the audio input and output. In Logic Studio, choose, Preferences -> Audio and choose the Firestudio for Recording and Playback.