If you are using the word theologian in the traditional sense, I'm not sure if Frederica Mathewes-Green counts (I won't judge her) but I can tell what she has to say on the topic in Welcome to the Orthodox Church.
I don't have the book with me or I'd quote it. However, she says the mind has two gears in which it can operate. In one, it is producing information by engaging in analytical thinking. In the other (the nous) it is receiving information and experiencing reality directly.
For example, take Sherlock Holmes. He uses powers of physical observation to gather facts and then use deductive "fleshly reason" to analyze these facts and draw conclusions. On the other hand, St. Mary of Egypt knew everything about Fr. Zosimas as soon as she laid eyes on him (possibly before, I do not know).
While Sherlock had to think in order to learn about others, St. Mary was of such purity that she simply experienced Fr. Zosimas and immediately experienced his entire life as well.
Everyone experiences things and gains insight by the nous in the same manner as St. Mary. When I return home from work, it's difficult to look at my children and not admire them simply and without contrivance. However, doing so teaches me nothing about them because sinners such as myself see through a glass darkly while the glass of St. Mary was polished, clear, and shining.
Frederica says that we can only use one of these gears at a time and that, as soon as you begin critically evaluating something, you stop experiencing it. This does not mean the nous is a magical device which, upon our access and after much striving, will immediately grant us all knowledge.
Anytime you stop analyzing and start experiencing, you are using your nous. The difference between ourselves and a great saint is that our nous is dirty and darkened and theirs is full of light. Also, that we tend toward neglect of it and exercise of the analytical mind.
There are of course many other mental faculties such as will, emotion, etc.