I've just created a new mapping using the Kontrol X1 MK2's MIDI mode to control decks C and D. I hope this proves useful and could save the need for 2 X1's.
The mapping replicates the default X1 MK2 controls pretty well, but there is room for improvement with a few functions.
If people with an X1 MK2 could have a look at the mapping and give some feedback that would be great.
Here is the link: 4 Decks X1 MK2