To connect the salinity probe to the DRDAQ its output would have to be 0-2.5 volts. If it is above this then the output would have to be reduced with a potential divider.
The LSB for the DRDAQ is 2.44 mV, if your convertor produces voltage changes above this then it should be OK.
To fix the convertor to the DRDAQ have a look at the section 'Making your own sensors' in the manual. If you do not have a copy of the manual one can be downloaded from here