The good news is, you’re not alone. I’ve had this show up recently with an old Project file that might have been generated from a version of Cubase earlier than version 6. The particulars are the same as what you’re seeing: no use of surround channels ever, no surround/multichannel bussing present… all stereo. I’m seeing a mixer filled with surround planners and no way to get rid of them. Removing and resetting output assignments doesn’t jog it into a fix. Somehow, the Project file has become corrupted with permenantly assigned surround panners.
This is the first time I’ve ever encountered this. The only thing I can point the finger at is that it’s happening in C10. Other Project files that were generated around the timeframe this one was generated, launch normally, so I don’t have a clue as to what sets this bug off or causes the corruption.
The only thing that you don’t make clear is if you’re seeing this with Projects recently created in C10 or if they were created from earlier Cubase versions. If the latter is true, then there is common ground between what you’re seeing and what I’m seeing.