Using high-level software for timing the time between scans in these kind of freqs is useless.
I always thought that the double-buffer mechanism was strictly an NI-DAQ thing, not something your board has to take care of by using hardware buffers.
It could be your old board is no longer supported by a recent NI-DAQ version, but old version should not be bad for your application. Just try the double-buffering and regularily read-in the new values (don't know the details, it has been a while since used last).