Hi Wayne,
For full attenuation, I think it will require external filter. There is link below that will point you to ADI filter wizard that might help you selecting some higher order filter to maximize pass band frequency.
FILTER WIZARD | Analog Devices
I am also attaching the AD77606 filtering model ( which can also be found on the AD7606 product page). This can help in designing the input filter for the AD7606.
Regards,
Jonathan