it doesn't matter. there are no bindings made specifically for the Axis X. K2 isn't in the business of making/selling bindings, so you won't see any K2 integrated ski/binding setups any time soon.
I have had good luck with Look, Rossignol, and Salomon bindings. But in today's market, any binding will work for you.
My Axis X have Salomon 912 Pe bindings, but only because my friend at the shop gave them to me for a good deal. I was going to get Marker Piston Control bindings.
Best value in bindings can be found 1 or 2 models below the "top of the line." At your weight, you won't need a binding that goes to DIN 14, so that helps you avoid the top bindings anyway.