The MOX (2011) file formats (.X4_) are not directly readable by the MODX (2018)

What you can do:
MOX files can be translated and opened with a MOXF (2013). If you can load your data to a MOXF, you then will be able to SAVE as a MOXF file format (.X6_). The MOXF has all the lookup tables to translate the older MOX data.
MOXF format (.X6A, .X6V, .X6G) file types can be read by the MODX and MONTAGE. This will allow you to translate User Voices, Performances, and User Arpeggios.

I've managed to get my MOX X4A file converted to a X6A file, whats the best way to import this to MODX? Currently when I perform live I use my MOX in Master mode which uses a variety of voices and performances.

The MODX can import either the 384 User Voices and 32 User Drum Kits, or the 256 Performances.

The MOX Master Mode will have no meaning in the MODX, neither will Song/Pattern Mixing programs.

With the .X6A file on a USB stick
Press [UTILITY] > “Contents” > “Load” > Set the “Content Type” = User or Library
Open the icon that represents your USB drive, find your .X6A file
Tap it... select to load either VOICES or PERFORMANCES.

Which you decide to do will depend on how many individual Voices and how many Performances you want to keep.
In general, the MODX is much more powerful than the MOX, you will probably do better to import the data you require and then find how you can improve it. There are far more controller assignment setups, and new effects and filters, etc., don’t limit your thinking to 9 years ago.

In your old MOX you were limited to 8 oscillators per instrument sound... there is no such limit in the MODX, because you can have 8 sets of 8 oscillators if you so desire.

In the MODX you were limited to 8 oscillators per instrument sound... there is no such limit in the MODX, because you can have 8 sets of 8 oscillators if you so desire.

Typo probably meant to write:

"In the MOX you were limited to 8 oscillators per instrument sound... there is no such limit in the MODX, because you can have 8 sets of 8 oscillators if you so desire."

I'm having trouble loading the file, it spends a few minutes loading then comes up with the error message "Illegal File" the person who converted it has confirmed it loads fine on their MOXF. I've also made sure my USB stick is formatted on my MODX before putting the file on it.

An “Illegal File” error means that the MODX cannot read the file. The reason is unclear. How was it prepared?

I've got Jamal's Flash in X6A format, this is also reading as an illegal file

File probably contains data that will not translate. Contact the author for updated version (MODX/MONTAGE)