I have a brand new Studio 68, but when I use it standalone (i.e. with no computer hooked up to the USB) with a stereo keyboard plugged in to line 1 and line 2, it outputs mono through the headphones and main outputs and line outputs (depending on Mon button). It doesn't matter which settings I use—the output is always mono.
If I attach my Mac via USB, and hook it to Garage Band, I see stereo in Garage Band. If I route the Garage Band output back through the Studio 68, then I can hear stereo from the Studio 68 (either headphone or via main or monitor through amp and speakers).
However, the main reason for using Studio 68 will be as a standalone mixer with occasional recording to the computer. Why can't I hear stereo while standalone (i.e. without the computer)?
Does anyone else observe this behavior?