How can I make 'rich chocolate' flavor? I am in the process of making a DIY Soylent meal replacement. I've tried Hershey's cocoa powder and it tastes awful.
Commercial manufacturers of flavored protein powders, shake powders, etc. make such tasty drinks. What substances and flavorings do they use?
For reference, my recipe was:

Oat flour
Flaxseed powder
Barley powder
Whey protein isolate
Acacia gum
Hershey's cocoa powder
Sugar

Subsequently I also tried adding nutmeg powder and cinnamon as suggested by some recipes on CompleteFoods. It didn't help.
I've read that the commercially available powders contain isomaltulose, maltodextrin, and xanthan gum. Do these have anything to do with how the drink tastes?
'Rich chocolate' does not have anything to do with richness. It's just a common phrase shake/powder sellers use for their whey protein/shakes.
How can I do this?
Edit: Got a hold of the ingredient list of the desired end result. Which ingredients make for the creaminess and richness, as if I were drinking a milk shake?
Frankly, Hershey's cocoa powder is low quality. Buy a higher quality cocoa. One objective measure is the cocoa fat content. 

This is from Harold McGee's Keys to Good Cooking, published by The Penguin Press, New York, 2010, p. 476:


  Higher-fat cocoas make richer dishes. To compare the fat contents of different brands, check their nutrition labels.