Hi tobsboy,
have you already tried another USB stick (formatted FAT32, best formatted directly on the keyboard)?
If you have exported the Instrument Info File (.n27) correctly (after installing the Flash ROM Expansion Module) on the Tyros5 and then imported it into the YEM, the available "Voice Wave Size" should appear with "... / 1023 MB" (when you click on the Tyros5 Install Target) Is this the case for you?
If so, the Expansion Module is obviously recognized correctly by the Tyros5, and the problem is probably elsewhere (possibly it could be the USB stick used or, as mentioned above, one or more Packs may be defective and must be downloaded again from Yamaha).
To make sure that the Expansion module is properly installed and not damaged, you could run a special internal test routine ("FLASH MEMORY EXPANSION MODULE CHECK").
You are welcome to contact me via PM (Personal Message) and I will send you detailed information about this test.
Best regards,
Chris