I'd just like to say that, contrary to my expectations due to the many woes expressed on using anything other than a Texas Instruments FW chip, I head a great experience recording with a Fireface 400.
At home I use an E-MU 1820M, but I had a thing on location and needed better quality and more tracks than the Fast Track Pro I have for my laptop. I borrowed a friend's Fireface 400. I recorded drums (9 tracks) and guitars (3 tracks) for three days and sent a lot of stuff over various outputs, without a single crash, dropout, pop or crackle. I did use the wall wart PSU because my laptop only has the 4-pin connector. I kept it at a mellow 128 samples (my I7 could do better I'm sure) because I was monitoring through Total Mix and didn't need to play any softsynths.
I think the key was in using the latest firmware for the Fireface and the correct latest driver for the J-Micron chip. This is NOT the one "windows update" installs by default, I had to go get it from J-Micron (I found this recommendation in the RME forum).
Just as a heads up for people struggling with this or wondering about their setup.
EDIT:
By the way this was tracking into projects that already had like 20 tracks of vocals, multiple softsynths, several other audio tracks and a ton of plugs and automation.