To replace a Mono file with a stereo file. You need to start with a stereo pair of tracks to process. You can either duplicate the mono file ant name the resulting identical pair with the .l .r convention and then place them on a stereo track. The other solution is to duplicate the playlist for the mono track, create another mono audio track and select the duplicate playlist. You would select both of these mono tracks when triggering the sample with SoundReplacer. You would set the output of SoundReplacer to Stereo and select a stereo track as your output setting.