Bad news -- this seems to be an inherent restriction for that particular digital module.
I tried replicating your system with simulated devices, saw the same error, and tried a number of additional DAQmx signal routing "tricks" to try to prevent it. None of them worked.
So I did some more thorough searching on the site here and found this. It looks like you'd need an additional digital module. Or perhaps a different one -- it sounds like the restriction is for "serial bidirectional modules". I'd venture that the high channel count is probably why the 9375 is serial (and thus restricted) rather than parallel (and perhaps *not* restricted?).
-Kevin P
CAUTION! New LabVIEW adopters -- it's too late for me, but you *can* save yourself. The new subscription policy for LabVIEW puts NI's hand in your wallet for the rest of your working life. Are you sure you're *that* dedicated to LabVIEW? (Summary of my reasons in this post, part of a voluminous thread of mostly complaints starting here).
