It's the Japanese market. I might give that a shot. I was first working on replacing the "subwoofer" and I was wondering how in the world people were fitting a 10'' sub in that spot with all this extra stuff. Now I realize that I'm in a unique situation.Which model are you working on? Japan or Middle East Market??
One possible option, get a sheet of cut-to-fit home HVAC foam filter
and install it over the air intake grill.