DSS Player Lite is a tool that allows you to play .DSS Files
DSS Player Lite is a free piece of software that allows the playback of .DSS files. The software itself is designed to be very basic and doesn't allow much other than playback. As a result there is no support for foot controls to be used and the software itself is unsupported.
OPDSupport recommends to trial the Olympus Dictation Management System Release 7 (ODMS R7) Transcription Module instead, as that is supported and it provides much more utility, control and ultimately allows you to playback .DS2 files - aswell as .WAV, .MP3 and .WMA files.
Check out this guide on how to start a trial of ODMS R7.