You can resolve this issue quickly. Change the rear speaker connections from left to right at the Onkyo, or Cinepro, whatever you are using to power the speakers. If the fault stays at the speaker, then that has to be the source of the problem. If it moves to the other side then your electronics are at fault.
If you are just using the Onkyo, then that is at fault. If you are using the Cinepro, then swap the connections to the Cinepro. If it stays with the speaker, then the Cinepro is the problem, if it moves then the Emo or the Onkyo or what ever you are using as the preamp is at fault.
You have a lot of equipment mentioned and your posts are vague and lack precision and clarity. Isolating this fault to the offending piece of equipment is simple applied logic on the basis of a simple experimental plan.