If your instruments have differential outputs, by all means use the differential input connection. Note that some DAQ devices require bias resistors on differential inputs if the data source cannot provide the small but necessary bias current. Check the manual for your device.
Thank you for the help. When connected the open (unused) terminals being scanned to COM all the gauges still responded to one voltage input. However, when I supplied a second voltage to another input each gauge worked independent. Thanks so much!