I spoke with Marantz about this because I am about to purchase this exact model and wanted to hear what they had to say. Basically the tech said there is no setting on the Marantz that has anything to do with aspect ratio. He suggested checking the settings on the DVD player. I imaine you have already done this, so I will be interested to see what you have to say about that.
Their support number is 1-800-654-6633.
Their support number is 1-800-654-6633.