7, welcome. As has been mentioned, generally two good subs(such as EP500s)would have an advantage in that they could be placed so as to help minimize fluctuations due to room modes. For example, placing them at the midpoints of the side walls, opposite each other, they'd be at a partial null for the room length mode and although they'd be at the maximum for the room width mode the phase relationships between the opposite walls would be opposite each other and would result in a partial cancellation of the width mode.
