If you have swapped interconnects (between source and power amp) and you have (in a separate test) swapped speakers with their respective cables (left channel to right side and right channel to left side) then you have eliminated your system as the source of the problem.
=> The only things that remain are your ears and the room!
(if your equipment was causing this the problem one of the above tests would have moved the image to the other side of center by one foot)
=> The only things that remain are your ears and the room!
(if your equipment was causing this the problem one of the above tests would have moved the image to the other side of center by one foot)