I just bought and installed the fireface 400 and I cannot explain how happy I am with the purchase.  I am running Windows Vista with an 8 core machine and 6MB of ram.  I previously had the Mackie Onyx 400f.  Not a bad unit.  There were some windows driver issues and my phantom power went out after a couple of years.  I wanted to take my studio to the next level and this has been a wonderful experience, especially after updating the drivers/firmware (which should be done immediately!!).  The sound is Amazing.  The software/drivers and hardware are solid.

Thank you RME