An answer to one question would be useful. We have a 32768Hz source already
on our board. We are presuming that this can be fed straight into XTAL1 for
the clock. Is this correct?
You can feed the clock source directly into pin XTAL1. Pin XTAL2 should be
left open (floating). The clock source should be able to directly drive the
AD7709. However, the clock source should be stable. The filter notches are
directly related to the clock so drift in the clock frequency will cause the
filter notches to drift also.