I am a bit crazy, so I spent too many hours doing some reverse engineering and lots and lots of trial-and-error work to achieve a very nice mapping of my Behringer DJ controllers.

Using a MOTU M4 audio interface, it makes a spectacular setup on an 12-inch iPad Pro (see photo).

My mapping were designed in a manner that allows any combination of the modules, with little redundancy of assignments and instant switching between any decks.  I believe I figured out the best use of the control surfaces, with a great balance between ease of use and efficiency.

Actually, it makes me think that the CMD controllers could now be the best one for anyone who use djay Pro (iPad or Mac) with a good 4-channel sound card / audio interface.

Especially that you can still find them at bargain prices.