In large bowl of electric mixer, combine 4 cups all-purpose flour, whole wheat flour, yeast, and salt; stir to blend dry ingredients thoroughly.

In a 1 1/2- to 2-quart saucepan, combine milk, the water, agave and oil; place over medium heat, stirring to blend well, until hot to touch (110° to 115°F). Add milk mixture to flour mixture. Mix to blend, then beat at medium speed until smooth and elastic (about 5 minutes). Stir in about 3/4 cup of the remaining all-purpose flour to make a soft dough. Turn dough out onto a board or pastry cloth coated with some of the remaining 1/2 to 1 cup flour. Knead until dough is smooth and satiny and small bubbles form just under surface (about 10 minutes), adding just enough flour to prevent dough from being sticky. Cover dough and let rest for 10 minutes.

Divide dough into two equal portions. Shape each into a loaf. Place shaped loaves in greased 4 1/2- by 8 1/2-inch loaf pans. Cover lightly with waxed paper or plastic wrap. Let rise in a warm place until doubled in bulk (40 to 45 minutes). Preheat oven to 375°F. Bake until loaves are well browned and sound hollow when tapped (30 to 45 minutes). Remove loaves from pans and let cool on wire racks.