If you just use the standard lightning to USB cable, you'll probably run into the problem of the ipad air complaining about the X5 drawing too much power and refusing to accept it.
You may need some sort of a cheap Chinese usb hub that tricks the ipad air into thinking the X5 consumes only very little power (as I did for the FiiO X3, see above). Or you go the expensive way and buy an original powered Belkin hub for the Ipad Air.
I don't know if this cheap solution is available for the lightning connector. So if you want to try my solution which will almost definitely work, you need a lightning to 30 pin (old Ipad connector) adapter. Then this cheap Chinese USB hub/card reader/Camera Kit from Ebay (sent directly from China - just search for Ipad camera kit usb hub on ebay, you'll find many cheap ones. And off you go.