Hi,
DS2 files are a proprietary format created when the Olympus DS-2400 is used to make dictations. After the dictation is created, the format can be converted to DSS or WAV format using the Olympus Standard software included with the DS-2400, which means you will have to request that the person creating dictations converts the files before sending them to you.
Try using DSS files in Express Scribe.
To convert files from the Olympus Standard player, have the user select the dictation(s) in the list, go to the File menu, select "Convert Dictation" and then click the Convert button.