Can I load only a couple voices from .x6a file into an user bank. When I look at the .x6a file on USB stick I don't see the individual files. I only want to overwrite a couple of USER files.

Place the USB stick into the “To Device” port
Press [FILE]
Press [F2] LOAD
Set the Load TYPE = Voice
Move the cursor to highlight your file’s name
Press [ENTER]

The file will ‘open’ to show you the lists of individual Voices in your MOXF
You can then target where in your User Bank you wish to place it (overwriting the destination)