The brochure and this image on Nissan's website would seem to indicate that the 2nd gen Rogue's come equipped with a second subwoofer.
After looking at the
FSM and this online parts list
http://www.nissanpartsdeal.com/parts-li ... eaker.html it appears that the brochure and picture are wrong, and there's only one subwoofer.
It's not unusual for a manufacturer to make changes to the final product after the literature has been printed, or the wrong info was put into the brochure and the discrepancy hasn't been addressed. I suspect they fully intended to have two subwoofers in the premium sound system, but for some reason weren't able to add the second one, and never updated the printed material.