A cursory Google search did not turn up any Panasonic camera with that model number. Are you sure that's correct?
With a VCR feed, I would think that you would want SD, as the source being fed to the camera's pass-through will be analog video tape. Am I missing something here?
Also, what Mode is set on the Pannie? [Since you use it in FCP, then I assume that it DOES have pass-through capabilities.]
You probably meant the AJ-HDX900 camcorder (yes?)
The capture options are HDV or DV (and while all HDV is HD, not all HD is HDV).
You have DVCProHD on that camcorder, which is not HDV. That being said, you'll probably want to just leave the capture set at "DV." Choose the Panasonic Then plug in the camera and start capturing.
IEEE 1394 (aka FireWire) is transmission only, so it will either losslessly transfer the footage to your computer or it will not.
One issue you may have is data rate. Depending on your shot settings, you'll need to be sure that your hard drive on your Mac can handle the throughput. But then, you'll probably know the answer to that right away if you start dropping frames like crazy.
Let me know if that works.