Patrick,
two links for good advice with the RME HDSP card:
Linux Journal: Using the Hammerfal HDSP on Linux by Peter Todd
http://www.linuxjournal.com/article.php?sid=7024&mode=thread&order=0
Installing and using a rme hammerfall dsp with linux by Dieb13:
http://pd.klingt.org/files/hdsp-howto.html
best,
d.