For 1.3 it was orginally on the roadmap to be able to fall back to a Definity/Audix over a PRI trunk. Then, 1.4 was going to work over an H323 trunk. That way you could have a core Definity and IP office systems in branches.
They took it out though, and no word that I've seen when they are going to put it back. This steps on the market for the S8300/G700. It's either because of that, or the less paranoid version says that they just wanted to work on bugs rather than new capabilities at this point.
Since Audix does not talk VOIP (it uses analog ports for the voice path, yes LAN just for signaling), I can see where IP office will never be able to use an Audix all by itself.