If you have LabVIEW RT 5.1, then you may use either NI-DAQ 6.5.2 or NI-DAQ 6.6. If you have LabVIEW RT 5.1.2, then you may use NI-DAQ 6.7, 6.8, 6.8.1, or 6.9 (NI-DAQ 6.9 is recommended). The upgrade from LabVIEW RT 5.1 to 5.1.2 is FREE(http://www.ni.com/upgrade).
Although we have not released LabVIEW RT 6.0 yet, it will be compatible with NI-DAQ 6.7, 6.8, 6.8.1, and 6.9. We recommend using the latest version, which is currently NI-DAQ 6.9. See the related KnowledgeBase article: