Here goes some strange advice. I got my fireface about a year ago, and couldnt get it to work for abou 2 months. I tried everything. Diferent fierwire cards (Recomended Lacie included), diferente computers, diferent nuendos. Everything, even RME was confused at the problems i was having.
Guess what, the firewire cable that came with the unit was totally f*ked. I would get levels on the progams software inputs and everything. I just couldnt record.
Changed the cable and never had a problem again. Not 1. Touch wood.
Anyway, this probably isnt your prob, but check it out anyway.