Preheat oven to 350 degrees. Oil a 9x11 inch baking pan with cooking spray.
Place amaranth in a heavy bottomed skillet over low heat. Stirring constantly, toast until the grains start to pop and turn golden, about 2-3 minutes. Transfer to a bowl and add cornmeal, flours, baking powder and baking soda. Mix well.
In another bowl, whisk together the oil, syrup, soymilk, apple juice, and salt, until blended and emulsified. (This may also be done in a blender.)
Pour the wet ingredients into the dry, stirring just until the dry ingredients are completely moistened. Pour the batter into the prepared baking dish and bake on the middle rack of the oven for 35-45 minutes [30 minutes works for me], or until the cornbread is firm to the touch and a toothpick comes out clean. Let cool before slicing.