Hi,
while there are USB to Ethernet adapters availible for computers, I don't think they will work with the Genos because lack of drivers and I think Yamaha themself only sell wireless adapters.
If you use the USB to Host connection, you can transfer music files with the Musicsoft downloader program However, I dont think you will be able to use YEM with the USB to Host connection and even if it would work, I can imagine it would be incredible slow.
I think your best bet is to either move your wireless router closer to the keyboard or get a wifi extender/repeter.
The other way would be to use a USB stick to transfer the files, but it's very nice to be able to transfer files without fiddling with USB sticks back and forth between the computer and Genos.
Best regards
/Jugge