"the Ketron doesn't know whats connected to the USB port when it boots"
no not now, but maybe with an OS modification....
or maybe build a new bottom for the A4 and A5, yes the entire bottom sheet metal
with a door w/screw positioned to easily access the HD
i'd pay $100 for that too
Leezone, not now and not never, there's only you wants a external drive, in the Western World, there are no OS modifications, Ketron never did work for NASA.