I agree with Marotta. (I can nearly hear the bodies hit the floor as they faint from the shock of that sentence :-)
It is true that epistemology and metaphysics are more fundamental than morality, but that doesn't mean they should be the nexus, the entry point, the common starting ground. Morality should be these because it ties in to, and is intricately bound to 'purpose.' Without morality we couldn't determine the objective purpose for a given context. And we can't form an individual purpose, or pursue it, without morality. Life is about sucessful actions, and morality is about purposeful actions.
Our health, at a certain level, is a requirement for going about our lives - and in that sense, fundamental, but unless it presents a problem we aren't going to be focused on it whereas morality, properly understood, is totally intertwined with the pursuit of the good life.
Just as health would be our primary focus only if it becomes a problem, we'd only focus on epistemology or metaphysics to straighten out thinking problems that we'd trace to those levels.
I suspect that psychology, particularly in terms of self-awareness, is a nexus in a different way, but just as fundamental to living a good life. Maybe we need to treat psychology more like we do morality, in the sense of being a set of principles that we should keep in mind (and thereby improve our process), and to treat morality a bit more like we do psychology, in the sense of grasping that its principles are directly tied to our individual success and happiness.