If I want to make these brownie more cake like, what ingredients should I add or increase. All that is required off of the box is 1/3 cup water, 1/3 cup vegetable oil and 1 egg.
I love the double chocolate. I would not try making the better by adding anything except maybe nuts, or marshmallows or even more chips I would not add more eggs or whatever they are the best. IMHO
I've found that if I replace the vegetable oil with applesauce when baking, the result is usually more cake like.
It's tough to do when you're starting from a mix. From scratch, I would generally recommend switching to butter, and creaming it with the sugar to help make some structure, but since that's not an option for you, the butter might not help.
At the very least, reduce the fat some (by 1-2 T) and add some baking powder for leavening (1/4 t?). Then give your batter a good whisking to aerate it before baking. Using butter instead of oil might still be in your best interest, but I'm not sure how well it would work mixing it in with the flour all at once...