Somewhere online I found a recipe for strawberry cake that's actually white cake with real strawberries and I think strawberry gelatin. That would work better, I think, with chocolate icing than the boxed strawberry.
It comes out pink, but tastes more like genuine strawberries than the mix.
Otherwise, I'd go for vanilla or a cheesecake frosting.
SAHM to Magnolia May (09/10) and Luke Russett (04/13) and wife and best friend to my airman.