Newbie here, just got an mx.
I wanted to verify a few things.
If I wish to load something new from the performance kit or live instruments pack, I realize I write into user patches?  What is I want to combine some from each?
If I like something, how do I keep it, but write over other user patches with something from another loaded pack?
Or can you really only use sounds from a pack one at a time?
Or do you have to purchase the total librarian to do that?

I used Total Librarian - MX Voice Editor from John Melas to save a voice to a file after having loaded the x5a file from user pack or external source.  I was then able to load that voice file and save it to user voice which is then stored inside the MX and can be called up in any performance.You can directly save it to a User voice as well.