In_shore, I never said that I knew for a fact that alu/MDF sandwich sounded good. I did say (twice at least) that it MIGHT sound good, because sometimes the effects of CLD transcend the sonics of the individual materials used in the sandwich. I suggested that you might be off base in condemning it out of hand. Or, have you in fact actually heard the Classic Direct? I didn't think so.
Why I did not use it: I lack the equipment and the know-how to make such a sandwich in the proper way so as to get the result one wants. I never thought of it. I took the more simple-minded approach of using slate. Then I found that slate in a sandwich with cherry or baltic birch sounds better than slate alone. Artisan and Porter are selling great beauty as well as solid hard woods. Dobbins is using proprietary materials in the Beat. At one point he referred to it as "man-made slate", or so I am told second hand. There IS such a thing, but I don't know that it has superior sonic properties. The proof of the pudding is only in the eating.