There isn't one, that's why!I don't think there is a stereo mix at all on my DVD-A of "Tigerlily". I tried it on my Pioneer 578 player and on my PC using either WinDVD 7 or Creative's DVD-A player and saw no option to play a stereo mix. It's only 24/96 5.1 or Dolby Digital 5.1
"the 5.1 stream with a downmix set at the MLP decoder".There isn't one, that's why!
As Cai rightly pointed out earlier the stereo is a downmix.
All that is in the Audio_TS is a single group, containing the 5.1 stream with a downmix set at the MLP encoder.