"The soul" is proposed as an actuality in the sense of substantive form. And, that "form" itself, is substantive is supported by his "Metaphysics". This allows for the proposition "the soul is our subject of study". — Metaphysician Undercover

I see how this all hangs together, thanks.

That reference to De Anima in the footnote does point to a particular expression of "self-consciousness":

It is necessary then that mind, since it thinks all things, should be uncontaminated, as Anaxagoras says, in order that it may be in control, that is, that it may know; for the intrusion of anything foreign hinders and obstructs it. Hence the mind, too, can have no characteristic except its capacity to receive. That part of the soul, then, which we call mind (by mind I mean that part by which the soul thinks and forms judgements) has no actual existence until it thinks. So it is unreasonable to suppose that it is mixed with the body; for in that case it would become somehow qualitative, e.g., hot or cold, or would even have some organ, as the sensitive faculty has; but in fact it has none. It has been well said that the soul is the place of forms, except that this does not apply to the soul as a whole, but only in its thinking capacity, and the forms occupy it not actually but only potentially. But that the perceptive and thinking faculties are not alike in their impassivity is obvious if we consider the sense organs and sensation. For the sense loses sensation under the stimulus of a too violent sensible object; e.g., of sound immediately after loud sounds, and neither seeing nor smelling is possible just after strong colours and scents; but when mind thinks the highly intelligible, it is not less able to think of slighter things, but even more able; for the faculty of sense is not apart from the body, whereas the mind is separable. But when the mind has become the several groups of its objects, as the learned man when active is said to do (and this happens, when he can exercise his function by himself), even then the mind is in a sense potential, though not quite in the same way as before it learned and discovered; moreover the mind is then capable of thinking itself. — De Anima, 429a 16, translated by W.S Hett

Aristotle's point in the quote from Parts of Animals is not an opposition to "materialism" as depicted by Gerson but a basis upon which to study material beings. While arguing for first principles and causality, Aristotle said this in regards to Empedocles:

For instance, when he is explaining what Bone is, he says not that it is any one of the Elements, or any two, or three, or even all of them, but that it is “the logos of the mixture” of the Elements. And it is clear that he would explain in the same way what Flesh and each of such parts is. Now the reason why earlier thinkers did not arrive at this method of procedure was that in their time there was no notion of “essence” and no way of defining “being.” The first to touch upon it was Democritus; and he did so, not because he thought it necessary for the study of Nature, but because he was carried away by the subject in hand and could not avoid it. In Socrates’ time an advance was made so far as the method was concerned; but at that time philosophers gave up the study of Nature. — Parts of Animals, 242a 20, translated by Peck and Forster

I am curious what Rödl will make of Aristotle's enthusiasm for empirical study while formulating his concept of "Idealism".