Using the bandpass sigma delta ADC in AD9874?

Yes it is possible if you operate the ADC clock at 20.8 MSPS such that the IF2 is centered at 2.6 MHz.  Also you can refer to page 38 of the datasheet that describes such an application where the mixer's LO port is fixed to a DC bias voltage such that one can still use the LNA input path for the 2.6 MHz IF signal.  Lastly, you may want to refer to the recently updated AD9864 datasheet (sister product of the AD9874) for an updated (more robust) SPI  initialization procedure. 

Yes it is possible if you operate the ADC clock at 20.8 MSPS such that the IF2 is centered at 2.6 MHz.  Also you can refer to page 38 of the datasheet that describes such an application where the mixer's LO port is fixed to a DC bias voltage such that one can still use the LNA input path for the 2.6 MHz IF signal.  Lastly, you may want to refer to the recently updated AD9864 datasheet (sister product of the AD9874) for an updated (more robust) SPI  initialization procedure.