Here's a link to info regarding the iRig MIX...
http://www.ikmultimedia.com/products/irigmix/I am not a fan of IK Multimedia's apps - mainly due to the pricing model they use, but as the mixer accepts any audio input you can use it however you see fit.
I personally like to use it with a single audio cable from my iPad to channel one input, then using the selector switch for single input, it splits the signal into two dual mono sources.
On all the other apps that I have tested (and since disregarded), any external mixer output sends Deck A to channel 1 (left hand side) and Deck B to channel 2 (right hand side)...but alas in CrossDJ for iPad it's Deck A to channel 2 (right hand side), Deck B to channel 1 (left hand side).
Due to this "issue" I route the audio from my iPad via a 3.5mm (male) to 3.5mm (male) cable into a custom splitter box (not rocket science), which has two outputs, which via 3.5mm (male) to 3.5mm (male) cables feed the mixer into channels 1 and 2.
Obviously in this setup I can swap over the output cables from the splitter to compensate, but it would be so much neater to just be able to make use of the one cable system into the mixer, then use the mixers internal signal splitter.
Simon