Thanks for your answer.
Why does flashing using USB cause problems? What kind of problems? Is there no other way to flash the drive than taking it out of its enclosure and connecting it via an IDE cable?
How do I manage to take out the drive? (Never done this before, just had worked with internal drives)
And where do I get the RPC1 patch for the H55N drive? I have already read that both drives use the same firmware, but I haven’t found any place where I could download a modified one. rpc1.org seems to be totally down.