A .DC file and a .CAL file are the same file format. You can typically rename the extension of these files and use them as the other file type.
In SCS900 / Siteworks we use the CAL to store the observation data (GPS / Control Point Pairs) and the DC file to store the results, however the CAL file contains the results and the control data as well. If all you have is the CAL file and you need a DC file - just rename it to a .DC or vice versa and you should be good to go - no need to wash it through TBC first.
Alan