I have the Celviano AP-700, not a grand hybrid, but it is very similar to the GP series.
In the earlier Casio digital piano models, there is USB device mode which makes the folders and files inside the piano visible to the computer connected through USB cable. I don't see that in AP-700 and the GP series user manual.
My question: is there a hidden / undocumented way to enable USB device mode for AP-700 and the GP series digital pianos?