In reply to:

The only other option is to mount them on the wall behind me, which is where my couch is backed up against. I don't know if that is a good idea.



Sounds like a pretty good place to me! I would still "experiment" by having a couple of people to hold the surronds at various places/heights before drilling into the wall, but that wall is in fact almost a "text book" location. Now that I learned that there is no dipolar elements in the QS surrounds , I would not care if they are facing the sides or towards the front, as long as they are to the side or a bit to the rear of the listener.