After looking, you can setup a 1756 remote rack to your FlexLogix Controller over ControlNet or EtherNet/IP and use the 1756-IF4FXOF2F/B modules. On the input configuration tab set the "Synchronize Module Inputs" check box in the lower right side of the tab. You are also able to use the "Archiving Connection" comms format which you may find useful if you are trying to do synchronized high speed (realative to a PLC) data collection.
Darren