garageband track output to mackie

I have a Mackie ProFX12v3. I'm using the USB to interface with my Macbook Pro. I have the MIDI / Preferences for both GB and the Mac set to ProFX, and while I can get everything else to play out through the Mackie, I CANNOT get the tracks to play out. I can switch seamlessly to the headphone jack and plug that into the 1/2 USB in channels 11/12 and that works. I can get the loops to play out with the USB 3/4 selected, but when I play the track audio, the light meters light up and are active, however no sound is being output through the mackie. Yes, I have engaged the 3/4 button. I can open up Audacity and it works fine. I can open my music and it works fine. The only thing that is NOT working is the track audio out. Track audio IN IS working and I can record through the USB just fine. It is only the track audio OUT which is not working. I have a workaround using the headphone jack out to the 1/2 USB, but this is annoying and has noise. Any help? Thanks!