My best DB has been (for 3 gallons)
3.5 lb Dark Munich
2 lb Light Munich
1.5 lb Pilsner malt
0.5 lb CaraMunich III
an ounce or two of Carafa or Midnight Wheat for color.
22 IBU of nobleish hops
Even though Munich II can convert itself, the pils malt is enzyme insurance and makes sure it finishes dry enough for me.