I`m a bit further on but still not working.
I tried the new null modem cable and the latest Dreamup (v1.3.3.4) and it seemed to detect the box but displayed the message "is not a valid integer value". the box then froze until unplugged and restarted.
I tried the browser method again. Finally got the firmware update page by putting the IP into the browser when the box was in the "stop" mode (i had previously let the box boot up, that is why it displayed the Enigma2 web interface page).
However when I selected the nfi file and hit return the browser tried to send it for a minute or two before displaying the "cannot display webpage" screen. I assume that there should be a screen saying "update completed" or something?
did you ever sort that flashing problem via web interface, because i have the same problem, i even changed the dreambox to a static ip bypassing dhcp and it still doesnt work...
only way is null modem cable which is long winded