Just did some nosing around on the net and it looks like the update requires the ARM board.
I checked my minimig and it's using firmware release YQ090421 which appears to be the latest without the ARM board.
If I'm wrong, PLEASE tell me where to find the update!!
Actually, I'm pretty sure I have written to ADFs before, but I know I have written to the .hdf file.
Anyway, HD support without the ARM is really silly slow, in fact my A1200 gets similar performance over the subway usb which is connected via clockport

Anyway, I needed a null-modem cable to flash the PIC (TinyBootloader). I'm sure I got all the files and details from minimig.net. You might ask around there. I'm not really a minimig expert
http://www.minimig.net/viewtopic.php?f=5&t=256 <- try there
Still, you would probably be best to get the arm because your ADFs will at least be in order, and you'll have vastly improved HD performance.
http://www.youtube.com/watch?v=eNWLtSWXtD8