From what I can gather from 30 seconds of googling, just to confirm you have it hooked up like this, correct?
Amiga 23-pin output --> Firecracker DB15 input
Firecracker DB23 output --> 15.75KHz compatible monitor
The card should pass-through unless it is activated (by the driver or some other Firecracker compatible software). Certain the monitor works correctly otherwise and the pass-through cable is the right one?