Use firmware 1.9.2.7-7f
To load this module, just copy it to a usb stick or harddisk.
By default, any usb storage device is mounted in /tmp/harddisk
so, if for example, you got the module in "module" folder, just write this in your asus shell prompt:
insmod /tmp/harddisk/module/usbserial.o
That's all.
Good luck!