In this case, since you are not familiar with the room or placement, it would likely be best to revisit this once you have some info about the room and placement. I would say, in all situations, the Duo and Sierra-2 will perform better off-axis as a center compared to the Sierra-1, due to the very wide dispersion of the RAAL ribbon. With a horizontal listening window of +/- 20 degrees, the Duo center would be the better choice. If you need wider than that window, the Sierra-2/2EX would likely be the better choice.