Do NOT upgrade to 6.1.3! My iPad's useless as an audio server now unless I buy an HRT iStreamer or the like. However I'll still have to confirm if the iPad Mini works with SPDIF adapters using 6.1.3, as I've seen it working but I don't know the iOS version, but basically all that will do is make me think that maybe the problem isn't that they blocked out USB Audio, but the .3 version doesn't work properly with the 30-pin devices. For all I know, even the iDevice-specific DACs don't work with my iPad anymore. Will have to wait until I can borrow one that isn't the NuForce (since it only works with iTunes).
My iPad 3 ("The New iPad") and Audioquest Dragonfly work very well together under iOS 6.1.3, including 96/24 and 88.2/24.
There might be more at play than just the OS version.