Look for the dot as Twenty8 mentions to confirm that the stereo track is being recorded. It will consist either of the monitor mix of chs 1-6 (duplicating the headphone output, and RCA outs when they are set to L/R) or of the digital input to be recorded separately from chs 1-6, depending on how you set it up. When activated, the stereo file is recorded simultaneously and in sync with the other channels. Its start and stop times will be identical to the other channels
Regardless of how you have the recorder set to write chs 1-6 files (mono, stereo, or polyfile) the stereo track file is always a 2 channel stereo file and will have "ST" in the file name. If you want to play back that file on the recorder, you need to push the MULTI/STEREO button on the top face, which switches the machine between multichannel and stereo mode. You cannot playback both the multichannel and stereo file simultaneously on the machine.