The quick answer is I dont know, but experiment, note the socket labels and only PLUG 1 USB Stick in and see what it comes up as, then do the same in the other socket.
The reason I chipped in is something odd with the Yamaha Operating System happens when you have 2 USB Sticks in at the same time, I have some memory registrations from John Beesley called Classical Magic, If there is only 1 plugged in you read them normally, if you have 2 plugged in at the same time you have to read the SAME information but from a different part of the USB, his instruction read as follows:
Insert the USB into the slot at the
right hand side of the keyboard panel.
If you have a second USB stick attached
to your instrument, the ‘Classical Magic ’
USB stick will be mounted as USB2 rather
than USB1. If this is the case, where available,
please select ‘USB2’ and ‘USB2
Version’ first for each of the steps below.
Someone here will know why this is !!
Cheers