To make a long story short, I was tired last night and not paying enough attention, and I used the IUW burn tool to flash u-boot.bin as the U0 in the 2852 firmware update.
This is very, very bad. Now I have in my possession a brick that buzzes non-stop when turned on. No button pressing combinations get around this, and I have not been able to connect via USB or to boot from SD card to recover it.
I am hoping someone has a solution for resetting the firmware or otherwise fixing the damage I have done.