Muddy hops flavor comes from too many varieties competing for dominance of flavor. Use a distinctively American variety for flavor and aroma, and a neutral bittering variety. One of the citrusy "C" varieties will work well in a flavor/aroma capacity, as will Amarillo.
Magnum is perfect for bittering. Just don't go too crazy on the IBUs.
+1 to the idea of a little dark crystal. 4 ounces should be perfect. As I wrote in the Wiki article, Amber needs a broad spectrum of Crystal-malt flavors.
That's also quite a lot of Aromatic and Biscuit, too much for this beer. I have trouble telling them apart, anyhow. Me, I'd keep the Biscuit and swap the Aromatic for an equal amount of Pale Malt.