I am also having a very similar issue as Oren. If I connect my audio mixer to the headphone/line out on my Mac Pro, the signal is fine. However, when I connect to the RCA outs on the Blackmagic card, I get the audio stutter, dropped frames, etc.
FCP 7.0.3
Mac OS 10.6.8
2 x 2.8 Quad-Core Xeon
6 GB DDR2 RAM (800 MHz)
NVIDIA GeForce 8800 GT (512 MB)
My capture scratch is a G Technology ES Pro, RAID 5, using a MiniSAS connection.