Well, I can give you my experience from when I was fiddling with my Panasonic recently, though I understand that other models in the range might behave differently...
- Since you only want stereo, set the bluray player to PCM.
- As far as I can tell, you only have the option to choose PCM or bitstream on the TVs internal tuner - choose PCM. On the HDMI inputs there are no options (on mine) and the soundtrack from those inputs are always output as stereo through optical, irrespective of the settings on the player.
Hope that helps.