So far, I've installed the HXC firmware via the USB cable method (the device now shows HXC when I power the unit on). It's a seven-segment unit. I've put my floppy images onto a USB stick along with the config file for index mode, plus the appropriate naming convention. This seems to be working just fine - when the USB stick is inserted I see the numbers corresponding to the images. I've also set the system family via the two-button menu to Akai (0C).
My jumper configuration is as indicated by the green line in this image, which I believe is correct:

Anyone able to let me know what I'm doing wrong? Is there some obvious step I've missed?
Thanks!