so after evaluating both the 5751 and 5752 adapter modules for the FlexRIO, it has become clear that the 32-channel adapter isn't going to work for us. We were not able to test it with the actual drift tubes but we did test it with a variety of input frequencies and wave forms. The impedance mismatch caused a significant distortion of input waveforms. We feel that using the 32-channel could cause a loss or distortion of drift tube pulses.
The 5751, on the other hand, reproduced input waveforms quite accurately. We think the 5751 is the safer option.