I missed this. 24-bits Differential with x128 PGA? Holy crap. I'm sure that's at a reduced sampling rate, but assuming a 2.048V reference, that's an ADC-step of 122 nV (nanoVolts) on that 24th bit on the end.
Needless to say, there'd be noise issues at that level. Extremely high precision, for the people who can design a high-precision circuit. Then again, you probably can run it at 16-bits or less (or something more reasonable / easier to do).