The best you can hope for is that Mackie will make the DL a MFi product such that other apps (Studio 6, Auria, etc.) could use the audio from the DL. The simpler solution would be to make it play with Audiobus. This of course would mean playing nice with other manufacturers software, probably not in their "I'll take all my marbles and go home" plan. A second look at core audio for iOS shows no restrictions on number of audio streams available for recording (within performance limitations) and playback as is demonstrated by apps such as Auria etc..
Jerry got your tracking number yet for the rack or will I beat you to it?