Is there an instuction manual for loading the additional sounds to the MOFX?

the Reference Manual explains loading to the MOXF. The Reference Manual is a PDF downloadable from the Official MOXF Download page.

And most libraries come with their own detailed instructions. We can’t give you more information without (reprinting all options) if you can give us the full name of the File, we can then tell what type of data it is, and we can tell you exactly the steps to take to load it.

The instructions for a .X6A file would be different if you wanted to load *all* of the data or if you wanted to load just a single Song, or Single Pattern, or a single Voice, or a single Performance, or a Bank of 128 Voices, etc., etc.