I agree with hercher about adding the Munich as long as you up the hop bill. If you "steeped" as he suggested (at 150 for ~30 minutes) you would essentially be mashing them, which is necessary for Munich. Also, I would add about 0.5 lbs of Crystal 60L (or any other crystal). Extract does already have carapils in it but thats not going to get you any cara flavor, just body and mouthfeel. And definitely replace 1 lb of DME with 1 lb of corn sugar. Extract brews tend to finish with a high FG because of all the unfermentables in the extract so the sugar will counteract that and dry the beer out
If you are doing a half boil and topping off I would double all of your hop amounts and move the 30 minute addition to 20 or 15. If you are doing a full boil I would just add 0.5-1 oz each to the Zythos and Cascade and move the Zythos to 15. And definitely dry hop! Use about 2 or 3 oz of any or all of the hops you are using in the boil.
Here is what I would do for a full boil (which you should definitely do if you can):
Batch Size: 5.5 g
Boil Volume: 7.25 g
Original Gravity: 1.065
Final Gravity: 1.016
ABV (standard): 6.4%
IBU (tinseth): 74.82
SRM (morey): 8.11
FERMENTABLES:
6.6 lb - Liquid Malt Extract - Light (65.3%)
1 lb - Dry Malt Extract - Pilsen (9.9%)
1 lb - Belgian - Munich (9.9%)
0.5 lb - American - Caramel / Crystal 60L (5%)
1 lb - Corn Sugar - Dextrose (9.9%)
HOPS:
1 oz - Centennial for 60 min, Type: Pellet, Use: Boil (AA 10, IBU: 34.77)
2 oz - Zythos for 15 min, Type: Pellet, Use: Boil (AA 11, IBU: 37.95)
2 oz - Cascade for 1 min, Type: Pellet, Use: Boil (AA 7, IBU: 2.1)
1 oz - Centennial for 7 days, Type: Pellet, Use: Dry Hop (AA 10)
1 oz - Zythos for 7 days, Type: Pellet, Use: Dry Hop (AA 11)
Hope this helps!