Here are a couple of videos the demonstrate some of the unique features of the new iConnectivity iConnectMIDI4+ audio/MIDI interface.
The first video, via MusicInclusive, takes a look how to send audio between two iPads directly, using the iConnectMIDI4+.
The video below, via Jordan Rudess, demostrates the flexibility of the iConnectMIDI4+, including using multiple keyboard controller sources going to multiple iOS device destinations.
The iConnectMIDI4+ has a street price of about $200. See the iConnectivity site for more info.