Solution
The XP4 and XJ4 connectors cannot be used to access the backplane trigger lines (PXI_TRIG <0..7>) directly. Doing this would require some additional electronics or software to access the signals correctly. This is unintended use of the PXI(e) chassis, and could cause damage.
Instead, NI recommends accessing the PXI_TRIG lines using one of the following methods:
Both of these options use PFI lines on the module to access the PXI_TRIG lines. Assuming that the module has at least 8 PFI lines, then each PXI_TRIG line can be exported simultaneously. Alternatively, the PFI lines can send a signal to the PXI(e) backplane once it has been appropriately connected to a PXI_TRIG line.