Kriston, I think it's great that you have gotten such insight into how your DS's brain is working! The revelation, alone, that he does better when he hears information than when he more silently just thinks the information, can be very helpful, I would think. Do you find that your DS, in general, learns well through listening?
My DS11 has some of the same issues I've seen you discuss before. I have always ruled out APD, even though DS11 has a long history of ear infections and seems to hear everything around him at the same volume, because he learns so well when things are read or discussed with him. So, what Inky wrote about visual processing difficulties is interesting to me (he has done visual therapy in the past for tracking and teaming issues).
Interestingly, I have always tried to have DS learn things using as many senses as possible. For example, when practicing spelling words I would have him write the words as well as say the letters aloud while he was writing so that he would see them, feel them (as he writes), and hear them. It seems to work. With him, reading aloud allows him to "check" what he is reading because he is more apt to notice if he read something incorrectly. For him this means that reading aloud is less fluent.
Anyway, enough about me!

Like I said, I think it's great that you've begun to figure out another piece of the puzzle! It seems like a real "aha" moment! What a fascinating, lovely kid you have there!