It's not possible to import the DD bank data - nor any of the payroll set up you will need to use QB for payroll.
In any case, 600 employees is probably too much for QB to handle well - especially when it comes to payroll tax forms, which are the most limiting part of payroll in QB, as they have relatively small dollar limits of "nine nines", or 9,999,999.99. If you have any totals for a period - including a year - for wages or taxes that are larger than that, the tax forms will choke and you'll have to do them manually.
