Gonk, Page 31 of the manual recommends leaving the default data format in AUTO since otherwise signals that are not in the selected format won't be recognized.

I had a problem like bbarden's in my red-dot 950. If I put a regular CD in the DVD player and set the 950 mode to stereo, the 950 played in stereo. If I then put a DTS CD in the player, the 950 played in stereo (not DTS), although I could switch to DTS manually. But if I played a DTS CD in DTS and then put a regular CD in the player, the 950 played it in PL II-C (not stereo or even DTS NEO) although I could manually switch it to stereo.