You could use your extracts to create a recipe for a porter or stout. Here's a stout I made a while ago:
3 lbs. plain light dry malt extract
3.3 lbs. dark malt extract syrup
1/2 lb. crystal malt (60L)
1/2 lb. dark roasted barley
1 oz. Columbus bittering hops (12.2)
2 oz. German Tradition whole hops (5.4)
Using your materials, you could add more dark roasted grains.
FYI, I've since learned to use speciality malts to add color, roasted flavors, etc. to darker beers, rather than dark extracts. The issue is that with dark extracts you have no control (or idea) over what is in your extract - with crystal, chocolate, and other speciality grains, you control what goes into your beer.
All of that being said, as long as you have the dark extract, you might as well use it. Hope this helps!