Drink 5 bottles of cough syrup. Roughly 1770 mg. See where that takes you.

As to your theory of H20 "amping" dextromethorphan...no. It doesn't. At all. Period. You're wrong. I DO know how it works and the short answer is that it doesn't.

As to the thing about Dextromethorphan and MDMA, that is absolutly true. It is now, however, a good idea.