Well, I downloaded the user manual for the Studio 68c, and it says it is fully backwards compatible with USB 2.0 and 3.0.
At first, I assumed that meant it had to be USB 3.1. You can't be BACKWARD compatible with USB 3.0 if you aren't 3.1.
I really hate this kind of marketing ambiguity. This spec matters. I have a bad feeling these new "c" models really are only USB 2.0 because if they were running at USB 3.1 that fact would be shouted by PreSonus from the mountain top.