Do you use the original factory bootloader 6.00? For USB you need a bootloader that is capable of booting an image from USB. For the SF1028 the only option I know of is the bootloader used with Titanit. Warning: bootloader changes are always risky and you may end up with reseller ID puzzles. I would stick to the image in flash; it is faster. The only reason to switch to USB would in my opinion be the ability to use factory firmware in flash and E2/Neutrino from USB.

Regards,

Audioniek.