Mark,

you are right, there are 2 flavours of DTS-ES and DD-EX - Discrete and Matrix. If the disc has a 6.1 soundtrack then Discrete mode will allow this disc to play in true 6.1, or 7.1 if you have 2 rear speakers (there are still only 6 channels of data, channels 6 and 7 are identical). Any normal 5.1 DVD can be played in Matrix mode where the rear channels are synthesized and play all of the in-phase (mono) content from the side surrounds with a phase lag (if I understand it correctly).

Stuart

My Home Theater