Hey Murali,
Here is a discussion forum thread that has already addressed this issue from the traditional NI-DAQ side.
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=50650000000800000048880000&ECategory=Measurement+Hardware.Multifunction+DAQ
With NI-DAQmx you can get and set the gain for specific SCXI channels using the DAQmx Channel Property Node->Analog Input:General Properties:Advanced:Gain:Gain Value Property.
I hope this helps out,
Joshua P.
Application Engineering
National Instruments