Invoice Approval based on the DFF fields

 Hi all,

 I have a issue as follows,

 I need separate invoice approval based on the value entered  in the DFF field.(i.e i have two values, One is head office and the other one is Supplies )so depending on these two values  i should have two approval workflow.where  head office approval should go in one path which is different to supplies.I have already created approval workflow based on the amount , where below 30k assistant accountant and 30k-50k Accountant and above 50k assistant finance manager and it is working fine .However i am unable to differentiate this based on the DFF field.Any help ?