I use DH chocolate cake mix with a box of pudding (powder form) and an extra egg.
As for able to be stacked. The supports and cake boards are what holds your top tiers up, not the cake. You could use angel food in a tierd cake, as long as you have the proper structural support.
I use the Durable Wedding/3D cake receipe in the "most saved" receipes but I use chocolate syrup in place of the water.
BTW: You can stack a cake made from straight mix. Stacked cakes are supported by supports not cake. Supports (dowels/straws and cardboard circles) is what supports your cake. Cake doesn't support cake so the receipe really isn't revelant.
The chocolate WASC receipe on this site is also very good as is the one on the Hershey's Cocoa can.
EDITED: leily guess I was typing my answer when you posted. 
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