I have a similar problem. Reaper immediately recognizes all four inputs from the Studio 68c. Studio One, however, doesn't accept inputs 3 and 4. It only has two inputs that I can move using the Audio I/O options. How do I get all four to work? This is quite embarrassing for PreSonus, to be honest. Reaper is working perfectly, but their own software is too buggy to get it right...