There is actually no need to, since the MOXF will read the .X3A file, as is!

Voice, Performance, Arpeggio, Mix Template, and Waveform data from the .X3A file, can be loaded by the MOXF. If you have data in the Sequencer, simply SAVE it as a SMF (Standard MIDI File), this is the standard way to move Midi sequence data between any two sequencers.

But if you want an .X6A version of that Motif XF ALL data file, load it into a MOXF and then make a backup using the MOXF.