I have an idea.
I reread the last segment of MB2 and learned two things. First of all, the metal Elend ate is never described more than a "bead of metal" or, as Vin said, it was the wrong color from atium. So, we cannot accurately know what color the metal is. In any case, it does not match any of the other metals Vin is familiar with.
Furthermore, the Well is not described "like liquid metal", but actually "liquid metal". And silvery colored. Now, here is my thought: Duralumin and Aluminum are Internal metals, and in that regard, they internally enhance Allomancy. The other ones could externally enhance Allomancy... or something.
Plus, anyone else find it odd that we only know of the metal Elend ate only occurred at the Well of Ascension? They could be... like, alloys of each other, considering their close proximity. One being pure and the other being the alloy, I mean.
It smells like atium. Atium, like this metal, is extremely rare and only seems to occur in one place. Very... unique.