take an hour or two, get some long xlr's, and just move those damn adams all around that room with a good ref recording playing, and have no regard for practical concerns such as 'mix position' or 'basic human esthetics'. just move them everywhere.
as you're doing this, move yourself around and listen to everything. make them really wide and sit twice as far back as you normally do. set them up catty-corner, set them up near the middle... go nuts, and listen to what's going on.
somewhere, somehow, you should find lots of places where the bass is deep, if uncontrolled. if you don't, the problem is not your room. i'm with thrill, a total dropoff sounds like something else is going on. even the tiniest rooms with the most horrendous nodes and nulls still have lots of audible energy sub-60, it's just untamed.
keep us posted. and the fact that a cone moves doesn't mean you'll hear it; just ask anyone who owns ns10's
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gregoire
del ubik