Don't you need a centertap balun so meet the common mode bias requirements of the ADC? Or else you need to deal with capactively coupling of the inputs which can also result in imbalance.

No not necessarily. A centertap balun or transformer is a good option but not imperative. You can easily feed the common mode voltage back into the analog inputs of the ADC by using a split termination. See slide 19 for example.

No not necessarily. A centertap balun or transformer is a good option but not imperative. You can easily feed the common mode voltage back into the analog inputs of the ADC by using a split termination. See slide 19 for example.