ok, yes, mixing the base with the acid would certainly make salts.
I don't recall whether this applies to mdma, but certainly with meth the excess acid can be removed by acetone crashing, which is much simpler than gassing.
anyway, citric and ascorbic acids, particularly the latter, are not the most stable organic acids. ascorbic acid is light, heat and air sensitive and degrades quite easily, citric acid is less unstable, but it could be better.
tartaric acid is commonly used as a counterion for many alkaloids. It is very stable for an organic acid, and very soluble in water in comparison the the other two.
don't grind them together dry, just mix up a proper molar ratio into some dH2O and shake vigourously with the base as is in the extraction solvent, separate and evaporate the water.
The proper molar ratio will be 1:1 for ascorbic and citric acids, and 2:1 for tartaric acid. Tartaric acid is a dihydroxy diacid and is twice as acidic as most other organic acids (which are largely mono-acids).