DO and the aggregates are looking at experience from difference POV so there seems to be a discrepancy. This is not the case, really. If you break down contact you have: external base (world) + internal base (body) + consciousness-class. Now in MN 44 or 43 consciousness is said to be inextricably bound with perception and feeling. So each act of contact pulls in form, perception, feeling and consciousness. And it is dependent on these other aggregates that volition functions for how can volition occur in a vacuum? If there is no information of any kind, what can volition do? Nothing, so volition cannot be said to exist without the information provided by the other four aggregates, and so it is conditioned there.
Now, the question become: "where does ignorance reside"? It is safe to say the ignorance resides, so to speak, with perception and feelings more than any of the other aggregates. Since volition rests on dependence of these two aggregates, and these two are heavily tainted by ignorance, then we see that volition is also dependent on ignorance.
DO describes the experiential order of how the aggregates come to be, while the aggregates are a division of the being that has come into functional categories.
Or so I see it.