Overrun-Underran buffers error and such?
Out your step1 program, does the digitize/play stream works?
EDIT- just noticed that you are using a ZIV . . . mhhh!
I have only very old memories, about VLAB Motion.
The only thing i remember now, that's a nightmare to configure properly (ZorroII limitation, FIFO bla, bla problems, SCSI settings and right HDs- AV compliant)