Wage Attachment Workbench and Employee Loans

Currently we are using a single declining balance DBA for Employee 401K Loans.  However, management wants to track payments of both the principal and interest on these loans instead of just the lump sum amount due and monthly deductions.  I read in the user guide that the Wage Attachment Workbench can be utilized for employee loans and see a place for Interest on the Amount Due tab.  However when I set up a new DBA for these loans and use a Source of Calc of K (Employee Loans) the Amount Due tab is not available in the Wage Attachment Workbench.