The 9403 transfers data serially to the backplane (modules with 8 or less lines have a dedicated line to the backplane for each input/output, modules with more than 8 lines must transfer data serially). Therefore, it cannot be used to route signals to counters (these are located on the backplane).
Support was added for clocked DIO operations on these "serial" modules back in DAQmx 9.3 (see here), but I believe this only applies to the newer generation of cDAQ chassis (e.g. 9178). Assuming this is the case, the 9403 can be used for software-timed operations only on the 9172 which I wouldn't think would be accurate enough for your intended application (although you didn't mention accuracy or timing requirements)
Your best bet is likely to purchase a parallel digital input module (like the 9401 or 9402) and use this instead so you can access the counters.
Best Regards,
John Passiak
