I also recently bought an iPad and have been playing around with Traktor DJ. From what I understood there is a way to get two stereo outputs by using a ‘hack’ with the Apple iPad Camera Connection Kit. This doesn’t solve the problem, however, of having to use your iPad as a mixer: the outputs can only be used as master and cue. Links to NI website with the info are below. Hope it helps!
http://www.native-instruments.com/en/products/traktor/traktor-for-ios/traktor-dj/
http://www.native-instruments.com/en/support/knowledge-base/show/986/
